diff --git a/CHANGELOG.md b/CHANGELOG.md
index cc87192..4fd96ae 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 # [unreleased]
 
+Major API changes for the time API. If you are using the time API, it is strongly recommended
+to check all the API changes.
+
 ## Fixed
 
 - CUC timestamp was fixed to include leap second corrections because it is based on the TAI
@@ -20,6 +23,17 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Added basic support conversions to the `time` library. Introduce new `chrono` and `timelib`
   feature gate
 
+## Changed
+
+- `UnixTimestamp::new` renamed to `UnixTimestamp::new_checked`.
+- `UnixTimestamp` now has a nanosecond subsecond precision. The `new` constructor now expects
+   nanoseconds as the second argument.
+- Added new `UnixTimestamp::new_subsec_millis` and `UnixTimestamp::new_subsec_millis_checked` API
+  to still allow creating a timestamp with only millisecond subsecond resolution.
+- `CcsdsTimeProvider` now has a new `subsecond_nanos` method in addition to a default
+  implementation for the `subsecond_millis` method.
+- `CcsdsTimeProvider::date_time` renamed to `CcsdsTimeProvider::chrono_date_time`
+
 # [v0.11.0-rc.0] 2024-03-04
 
 ## Added
diff --git a/Cargo.toml b/Cargo.toml
index c0333c0..c0d6a8d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -48,8 +48,9 @@ optional = true
 version = "0.2"
 default-features = false
 
-[dev-dependencies.postcard]
-version = "1"
+[dev-dependencies]
+postcard = "1"
+chrono = "0.4"
 
 [features]
 default = ["std"]
diff --git a/src/time/cds.rs b/src/time/cds.rs
index fcb3a72..f83a908 100644
--- a/src/time/cds.rs
+++ b/src/time/cds.rs
@@ -4,20 +4,40 @@
 //! The core data structure to do this is the [TimeProvider] struct and the
 //! [get_dyn_time_provider_from_bytes] function to retrieve correct instances of the
 //! struct from a bytestream.
-use super::*;
 use crate::private::Sealed;
-#[cfg(feature = "alloc")]
-use alloc::boxed::Box;
-#[cfg(feature = "chrono")]
-use chrono::Datelike;
-#[cfg(feature = "alloc")]
-use core::any::Any;
+use crate::ByteConversionError;
 use core::cmp::Ordering;
-use core::fmt::Debug;
+use core::fmt::{Debug, Display, Formatter};
 use core::ops::{Add, AddAssign};
 use core::time::Duration;
+
 use delegate::delegate;
 
+#[cfg(feature = "std")]
+use super::StdTimestampError;
+#[cfg(feature = "std")]
+use std::error::Error;
+#[cfg(feature = "std")]
+use std::time::{SystemTime, SystemTimeError};
+
+#[cfg(feature = "chrono")]
+use chrono::Datelike;
+
+#[cfg(feature = "alloc")]
+use super::ccsds_time_code_from_p_field;
+#[cfg(feature = "alloc")]
+use alloc::boxed::Box;
+#[cfg(feature = "alloc")]
+use core::any::Any;
+
+#[cfg(feature = "serde")]
+use serde::{Serialize, Deserialize};
+
+use super::{
+    ccsds_to_unix_days, unix_to_ccsds_days, CcsdsTimeCodes, CcsdsTimeProvider, TimeReader,
+    TimeWriter, TimestampError, UnixTimestamp, MS_PER_DAY, SECONDS_PER_DAY,
+};
+
 /// Base value for the preamble field for a time field parser to determine the time field type.
 pub const P_FIELD_BASE: u8 = (CcsdsTimeCodes::Cds as u8) << 4;
 pub const MIN_CDS_FIELD_LEN: usize = 7;
@@ -165,7 +185,6 @@ pub struct TimeProvider<DaysLen: ProvidesDaysLength = DaysLen16Bits> {
     pfield: u8,
     ccsds_days: DaysLen::FieldType,
     ms_of_day: u32,
-    // submillis_precision: SubmillisPrecision,
     submillis: u32,
     /// This is not strictly necessary but still cached because it significantly simplifies the
     /// calculation of [`DateTime<Utc>`].
@@ -195,36 +214,47 @@ trait CdsConverter: CdsCommon {
 struct ConversionFromUnix {
     ccsds_days: u32,
     ms_of_day: u32,
+    submilis_prec: SubmillisPrecision,
+    submillis: u32,
     /// This is a side-product of the calculation of the CCSDS days. It is useful for
     /// re-calculating the datetime at a later point and therefore supplied as well.
     unix_days_seconds: i64,
 }
 
 impl ConversionFromUnix {
-    fn new(unix_seconds: i64, subsec_millis: u32) -> Result<Self, TimestampError> {
+    fn new(
+        unix_seconds: i64,
+        subsec_nanos: u32,
+        precision: SubmillisPrecision,
+    ) -> Result<Self, TimestampError> {
         let (unix_days, secs_of_day) = calc_unix_days_and_secs_of_day(unix_seconds);
         let ccsds_days = unix_to_ccsds_days(unix_days);
-        if ccsds_days == 0 && (secs_of_day > 0 || subsec_millis > 0) || ccsds_days < 0 {
-            let millis = if unix_seconds < 0 {
-                unix_seconds * 1000 - subsec_millis as i64
-            } else {
-                unix_seconds * 1000 + subsec_millis as i64
-            };
+        if ccsds_days == 0 && (secs_of_day > 0 || subsec_nanos > 0) || ccsds_days < 0 {
             return Err(TimestampError::DateBeforeCcsdsEpoch(
-                Utc.timestamp_millis_opt(millis).unwrap(),
+                UnixTimestamp::new_checked(unix_seconds, subsec_nanos)
+                    .expect("unix timestamp creation failed"),
             ));
         }
+        let ms_of_day = secs_of_day * 1000 + subsec_nanos / 10_u32.pow(6);
+
+        let submillis = match precision {
+            SubmillisPrecision::Microseconds => (subsec_nanos / 1_000) % 1000,
+            SubmillisPrecision::Picoseconds => (subsec_nanos % 10_u32.pow(6)) * 1000,
+            _ => 0,
+        };
         Ok(Self {
             ccsds_days: unix_to_ccsds_days(unix_days) as u32,
-            ms_of_day: secs_of_day * 1000 + subsec_millis,
+            ms_of_day,
             unix_days_seconds: unix_days * SECONDS_PER_DAY as i64,
+            submilis_prec: precision,
+            submillis,
         })
     }
 }
 
 impl CdsCommon for ConversionFromUnix {
     fn submillis_precision(&self) -> SubmillisPrecision {
-        SubmillisPrecision::Absent
+        self.submilis_prec
     }
 
     fn ms_of_day(&self) -> u32 {
@@ -236,7 +266,7 @@ impl CdsCommon for ConversionFromUnix {
     }
 
     fn submillis(&self) -> u32 {
-        0
+        self.submillis
     }
 }
 
@@ -246,13 +276,13 @@ impl CdsConverter for ConversionFromUnix {
     }
 }
 /// Helper struct which generates fields for the CDS time provider from a datetime.
-struct ConversionFromDatetime {
+struct ConversionFromChronoDatetime {
     unix_conversion: ConversionFromUnix,
     submillis_prec: SubmillisPrecision,
     submillis: u32,
 }
 
-impl CdsCommon for ConversionFromDatetime {
+impl CdsCommon for ConversionFromChronoDatetime {
     fn submillis_precision(&self) -> SubmillisPrecision {
         self.submillis_prec
     }
@@ -269,7 +299,7 @@ impl CdsCommon for ConversionFromDatetime {
     }
 }
 
-impl CdsConverter for ConversionFromDatetime {
+impl CdsConverter for ConversionFromChronoDatetime {
     delegate! {to self.unix_conversion { fn unix_days_seconds(&self) -> i64; }}
 }
 
@@ -286,27 +316,38 @@ fn calc_unix_days_and_secs_of_day(unix_seconds: i64) -> (i64, u32) {
     (unix_days, secs_of_day as u32)
 }
 
-impl ConversionFromDatetime {
-    fn new(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+#[cfg(feature = "chrono")]
+impl ConversionFromChronoDatetime {
+    fn new(dt: &chrono::DateTime<chrono::Utc>) -> Result<Self, TimestampError> {
         Self::new_generic(dt, SubmillisPrecision::Absent)
     }
 
-    fn new_with_submillis_us_prec(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+    fn new_with_submillis_us_prec(
+        dt: &chrono::DateTime<chrono::Utc>,
+    ) -> Result<Self, TimestampError> {
         Self::new_generic(dt, SubmillisPrecision::Microseconds)
     }
 
-    fn new_with_submillis_ps_prec(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+    fn new_with_submillis_ps_prec(
+        dt: &chrono::DateTime<chrono::Utc>,
+    ) -> Result<Self, TimestampError> {
         Self::new_generic(dt, SubmillisPrecision::Picoseconds)
     }
 
-    fn new_generic(dt: &DateTime<Utc>, prec: SubmillisPrecision) -> Result<Self, TimestampError> {
+    #[cfg(feature = "chrono")]
+    fn new_generic(
+        dt: &chrono::DateTime<chrono::Utc>,
+        prec: SubmillisPrecision,
+    ) -> Result<Self, TimestampError> {
         // The CDS timestamp does not support timestamps before the CCSDS epoch.
         if dt.year() < 1958 {
-            return Err(TimestampError::DateBeforeCcsdsEpoch(*dt));
+            return Err(TimestampError::DateBeforeCcsdsEpoch(UnixTimestamp::from(
+                *dt,
+            )));
         }
         // The contained values in the conversion should be all positive now
         let unix_conversion =
-            ConversionFromUnix::new(dt.timestamp(), dt.timestamp_subsec_millis())?;
+            ConversionFromUnix::new(dt.timestamp(), dt.timestamp_subsec_nanos(), prec)?;
         let mut submillis = 0;
         match prec {
             SubmillisPrecision::Microseconds => {
@@ -351,7 +392,8 @@ impl ConversionFromNow {
         let epoch = now.as_secs();
         // This should always return a value with valid (non-negative) CCSDS days,
         // so it is okay to unwrap
-        let unix_conversion = ConversionFromUnix::new(epoch as i64, now.subsec_millis()).unwrap();
+        let unix_conversion =
+            ConversionFromUnix::new(epoch as i64, now.subsec_nanos(), prec).unwrap();
         let mut submillis = 0;
 
         match prec {
@@ -589,20 +631,6 @@ impl<ProvidesDaysLen: ProvidesDaysLength> TimeProvider<ProvidesDaysLen> {
         self.calc_unix_seconds(unix_days_seconds, ms_of_day);
     }
 
-    fn calc_ns_since_last_second(&self) -> u32 {
-        let mut ns_since_last_sec = (self.ms_of_day % 1000) * 10_u32.pow(6);
-        match self.submillis_precision() {
-            SubmillisPrecision::Microseconds => {
-                ns_since_last_sec += self.submillis() * 1000;
-            }
-            SubmillisPrecision::Picoseconds => {
-                ns_since_last_sec += self.submillis() / 1000;
-            }
-            _ => (),
-        }
-        ns_since_last_sec
-    }
-
     #[inline]
     fn calc_unix_seconds(&mut self, mut unix_days_seconds: i64, ms_of_day: u32) {
         let seconds_of_day = (ms_of_day / 1000) as i64;
@@ -611,35 +639,11 @@ impl<ProvidesDaysLen: ProvidesDaysLength> TimeProvider<ProvidesDaysLen> {
         } else {
             unix_days_seconds += seconds_of_day;
         }
-        self.unix_stamp = UnixTimestamp::const_new(unix_days_seconds, (ms_of_day % 1000) as u16);
-    }
-
-    #[cfg(feature = "chrono")]
-    fn calc_chrono_date_time(
-        &self,
-        ns_since_last_second: u32,
-    ) -> Option<chrono::DateTime<chrono::Utc>> {
-        assert!(
-            ns_since_last_second < 10_u32.pow(9),
-            "Invalid MS since last second"
-        );
-        if let LocalResult::Single(val) =
-            Utc.timestamp_opt(self.unix_stamp.unix_seconds, ns_since_last_second)
-        {
-            return Some(val);
+        let mut subsec_nanos = (ms_of_day % 1000) * 10_u32.pow(6);
+        if let Some(precision) = self.precision_as_ns() {
+            subsec_nanos += precision;
         }
-        None
-    }
-
-    #[cfg(feature = "timelib")]
-    fn calc_timelib_date_time(
-        &self,
-        ns_since_last_second: u32,
-    ) -> Result<time::OffsetDateTime, time::error::ComponentRange> {
-        Ok(
-            time::OffsetDateTime::from_unix_timestamp(self.unix_stamp.unix_seconds)?
-                + time::Duration::nanoseconds(ns_since_last_second.into()),
-        )
+        self.unix_stamp = UnixTimestamp::new(unix_days_seconds, subsec_nanos);
     }
 
     fn length_check(&self, buf: &[u8], len_as_bytes: usize) -> Result<(), TimestampError> {
@@ -674,36 +678,43 @@ impl<ProvidesDaysLen: ProvidesDaysLength> TimeProvider<ProvidesDaysLen> {
         Ok(provider)
     }
 
+    #[cfg(feature = "chrono")]
     fn from_dt_generic(
-        dt: &DateTime<Utc>,
+        dt: &chrono::DateTime<chrono::Utc>,
         days_len: LengthOfDaySegment,
     ) -> Result<Self, TimestampError> {
-        let conv_from_dt = ConversionFromDatetime::new(dt)?;
+        let conv_from_dt = ConversionFromChronoDatetime::new(dt)?;
         Self::generic_from_conversion(days_len, conv_from_dt)
     }
 
+    #[cfg(feature = "chrono")]
     fn from_dt_generic_us_prec(
-        dt: &DateTime<Utc>,
+        dt: &chrono::DateTime<chrono::Utc>,
         days_len: LengthOfDaySegment,
     ) -> Result<Self, TimestampError> {
-        let conv_from_dt = ConversionFromDatetime::new_with_submillis_us_prec(dt)?;
+        let conv_from_dt = ConversionFromChronoDatetime::new_with_submillis_us_prec(dt)?;
         Self::generic_from_conversion(days_len, conv_from_dt)
     }
 
+    #[cfg(feature = "chrono")]
     fn from_dt_generic_ps_prec(
-        dt: &DateTime<Utc>,
+        dt: &chrono::DateTime<chrono::Utc>,
         days_len: LengthOfDaySegment,
     ) -> Result<Self, TimestampError> {
-        let conv_from_dt = ConversionFromDatetime::new_with_submillis_ps_prec(dt)?;
+        let conv_from_dt = ConversionFromChronoDatetime::new_with_submillis_ps_prec(dt)?;
         Self::generic_from_conversion(days_len, conv_from_dt)
     }
 
     fn from_unix_generic(
         unix_stamp: &UnixTimestamp,
         days_len: LengthOfDaySegment,
+        submillis_prec: SubmillisPrecision,
     ) -> Result<Self, TimestampError> {
-        let conv_from_dt =
-            ConversionFromUnix::new(unix_stamp.unix_seconds, unix_stamp.subsecond_millis as u32)?;
+        let conv_from_dt = ConversionFromUnix::new(
+            unix_stamp.unix_seconds,
+            unix_stamp.subsecond_nanos,
+            submillis_prec,
+        )?;
         Self::generic_from_conversion(days_len, conv_from_dt)
     }
 
@@ -818,7 +829,10 @@ impl TimeProvider<DaysLen24Bits> {
     /// This function will return [TimestampError::DateBeforeCcsdsEpoch] or
     /// [TimestampError::Cds] if the time is before the CCSDS epoch (1958-01-01T00:00:00+00:00)
     /// or the CCSDS days value exceeds the allowed bit width (24 bits).
-    pub fn from_dt_with_u24_days(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+    #[cfg(feature = "chrono")]
+    pub fn from_dt_with_u24_days(
+        dt: &chrono::DateTime<chrono::Utc>,
+    ) -> Result<Self, TimestampError> {
         Self::from_dt_generic(dt, LengthOfDaySegment::Long24Bits)
     }
 
@@ -829,19 +843,26 @@ impl TimeProvider<DaysLen24Bits> {
     /// This function will return [TimestampError::DateBeforeCcsdsEpoch] or
     /// [TimestampError::Cds] if the time is before the CCSDS epoch (1958-01-01T00:00:00+00:00)
     /// or the CCSDS days value exceeds the allowed bit width (24 bits).
-    pub fn from_unix_secs_with_u24_days(
+    pub fn from_unix_stamp_with_u24_days(
         unix_stamp: &UnixTimestamp,
+        submillis_prec: SubmillisPrecision,
     ) -> Result<Self, TimestampError> {
-        Self::from_unix_generic(unix_stamp, LengthOfDaySegment::Long24Bits)
+        Self::from_unix_generic(unix_stamp, LengthOfDaySegment::Long24Bits, submillis_prec)
     }
 
     /// Like [Self::from_dt_with_u24_days] but with microsecond sub-millisecond precision.
-    pub fn from_dt_with_u24_days_us_precision(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+    #[cfg(feature = "chrono")]
+    pub fn from_dt_with_u24_days_us_precision(
+        dt: &chrono::DateTime<chrono::Utc>,
+    ) -> Result<Self, TimestampError> {
         Self::from_dt_generic_us_prec(dt, LengthOfDaySegment::Long24Bits)
     }
 
     /// Like [Self::from_dt_with_u24_days] but with picoseconds sub-millisecond precision.
-    pub fn from_dt_with_u24_days_ps_precision(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+    #[cfg(feature = "chrono")]
+    pub fn from_dt_with_u24_days_ps_precision(
+        dt: &chrono::DateTime<chrono::Utc>,
+    ) -> Result<Self, TimestampError> {
         Self::from_dt_generic_ps_prec(dt, LengthOfDaySegment::Long24Bits)
     }
 
@@ -898,7 +919,10 @@ impl TimeProvider<DaysLen16Bits> {
     /// This function will return a [TimestampError::DateBeforeCcsdsEpoch] or a
     /// [TimestampError::Cds] if the time is before the CCSDS epoch (01-01-1958 00:00:00) or
     /// the CCSDS days value exceeds the allowed bit width (16 bits).
-    pub fn from_dt_with_u16_days(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+    #[cfg(feature = "chrono")]
+    pub fn from_dt_with_u16_days(
+        dt: &chrono::DateTime<chrono::Utc>,
+    ) -> Result<Self, TimestampError> {
         Self::from_dt_generic(dt, LengthOfDaySegment::Short16Bits)
     }
 
@@ -916,19 +940,26 @@ impl TimeProvider<DaysLen16Bits> {
     /// This function will return [TimestampError::DateBeforeCcsdsEpoch] or
     /// [TimestampError::Cds] if the time is before the CCSDS epoch (1958-01-01T00:00:00+00:00)
     /// or the CCSDS days value exceeds the allowed bit width (24 bits).
-    pub fn from_unix_secs_with_u16_days(
+    pub fn from_unix_stamp_with_u16_days(
         unix_stamp: &UnixTimestamp,
+        submillis_prec: SubmillisPrecision,
     ) -> Result<Self, TimestampError> {
-        Self::from_unix_generic(unix_stamp, LengthOfDaySegment::Short16Bits)
+        Self::from_unix_generic(unix_stamp, LengthOfDaySegment::Short16Bits, submillis_prec)
     }
 
     /// Like [Self::from_dt_with_u16_days] but with microsecond sub-millisecond precision.
-    pub fn from_dt_with_u16_days_us_precision(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+    #[cfg(feature = "chrono")]
+    pub fn from_dt_with_u16_days_us_precision(
+        dt: &chrono::DateTime<chrono::Utc>,
+    ) -> Result<Self, TimestampError> {
         Self::from_dt_generic_us_prec(dt, LengthOfDaySegment::Short16Bits)
     }
 
     /// Like [Self::from_dt_with_u16_days] but with picoseconds sub-millisecond precision.
-    pub fn from_dt_with_u16_days_ps_precision(dt: &DateTime<Utc>) -> Result<Self, TimestampError> {
+    #[cfg(feature = "chrono")]
+    pub fn from_dt_with_u16_days_ps_precision(
+        dt: &chrono::DateTime<chrono::Utc>,
+    ) -> Result<Self, TimestampError> {
         Self::from_dt_generic_ps_prec(dt, LengthOfDaySegment::Short16Bits)
     }
 
@@ -1140,20 +1171,22 @@ impl AddAssign<Duration> for TimeProvider<DaysLen24Bits> {
     }
 }
 
-impl TryFrom<DateTime<Utc>> for TimeProvider<DaysLen16Bits> {
+#[cfg(feature = "chrono")]
+impl TryFrom<chrono::DateTime<chrono::Utc>> for TimeProvider<DaysLen16Bits> {
     type Error = TimestampError;
 
-    fn try_from(dt: DateTime<Utc>) -> Result<Self, Self::Error> {
-        let conversion = ConversionFromDatetime::new(&dt)?;
+    fn try_from(dt: chrono::DateTime<chrono::Utc>) -> Result<Self, Self::Error> {
+        let conversion = ConversionFromChronoDatetime::new(&dt)?;
         Self::generic_from_conversion(LengthOfDaySegment::Short16Bits, conversion)
     }
 }
 
-impl TryFrom<DateTime<Utc>> for TimeProvider<DaysLen24Bits> {
+#[cfg(feature = "chrono")]
+impl TryFrom<chrono::DateTime<chrono::Utc>> for TimeProvider<DaysLen24Bits> {
     type Error = TimestampError;
 
-    fn try_from(dt: DateTime<Utc>) -> Result<Self, Self::Error> {
-        let conversion = ConversionFromDatetime::new(&dt)?;
+    fn try_from(dt: chrono::DateTime<chrono::Utc>) -> Result<Self, Self::Error> {
+        let conversion = ConversionFromChronoDatetime::new(&dt)?;
         Self::generic_from_conversion(LengthOfDaySegment::Long24Bits, conversion)
     }
 }
@@ -1176,26 +1209,14 @@ impl<ProvidesDaysLen: ProvidesDaysLength> CcsdsTimeProvider for TimeProvider<Pro
         self.unix_stamp.unix_seconds
     }
     #[inline]
-    fn subsecond_millis(&self) -> u16 {
-        self.unix_stamp.subsecond_millis
+    fn subsecond_nanos(&self) -> u32 {
+        self.unix_stamp.subsecond_nanos
     }
 
     #[inline]
     fn unix_stamp(&self) -> UnixTimestamp {
         self.unix_stamp
     }
-
-    #[cfg(feature = "chrono")]
-    #[cfg_attr(doc_cfg, doc(cfg(feature = "chrono")))]
-    fn chrono_date_time(&self) -> Option<chrono::DateTime<chrono::Utc>> {
-        self.calc_chrono_date_time(self.calc_ns_since_last_second())
-    }
-
-    #[cfg(feature = "timelib")]
-    #[cfg_attr(doc_cfg, doc(cfg(feature = "timelib")))]
-    fn timelib_date_time(&self) -> Result<time::OffsetDateTime, time::error::ComponentRange> {
-        self.calc_timelib_date_time(self.calc_ns_since_last_second())
-    }
 }
 
 impl TimeReader for TimeProvider<DaysLen16Bits> {
@@ -1330,6 +1351,7 @@ impl TryFrom<TimeProvider<DaysLen24Bits>> for TimeProvider<DaysLen16Bits> {
 mod tests {
     use super::*;
     use crate::time::TimestampError::{ByteConversion, InvalidTimeCode};
+    use crate::time::{UnixTimestamp, DAYS_CCSDS_TO_UNIX, MS_PER_DAY};
     use crate::ByteConversionError::{FromSliceTooSmall, ToSliceTooSmall};
     use alloc::string::ToString;
     use chrono::{Datelike, NaiveDate, Timelike};
@@ -1345,13 +1367,13 @@ mod tests {
             unix_stamp.unix_seconds,
             (DAYS_CCSDS_TO_UNIX * SECONDS_PER_DAY as i32) as i64
         );
-        let subsecond_millis = unix_stamp.subsecond_millis;
+        let subsecond_millis = unix_stamp.subsecond_nanos;
         assert_eq!(subsecond_millis, 0);
         assert_eq!(
             time_stamper.submillis_precision(),
             SubmillisPrecision::Absent
         );
-        assert_eq!(time_stamper.subsecond_millis(), 0);
+        assert_eq!(time_stamper.subsecond_nanos(), 0);
         assert_eq!(time_stamper.ccdsd_time_code(), CcsdsTimeCodes::Cds);
         assert_eq!(
             time_stamper.p_field(),
@@ -1382,8 +1404,10 @@ mod tests {
         assert_eq!(date_time.minute(), 0);
         assert_eq!(date_time.second(), 0);
         let time_stamper = TimeProvider::new_with_u16_days((-DAYS_CCSDS_TO_UNIX) as u16, 40);
+        assert_eq!(time_stamper.subsecond_nanos(), 40 * 10_u32.pow(6));
         assert_eq!(time_stamper.subsecond_millis(), 40);
         let time_stamper = TimeProvider::new_with_u16_days((-DAYS_CCSDS_TO_UNIX) as u16, 1040);
+        assert_eq!(time_stamper.subsecond_nanos(), 40 * 10_u32.pow(6));
         assert_eq!(time_stamper.subsecond_millis(), 40);
     }
 
@@ -1565,7 +1589,7 @@ mod tests {
 
     fn generic_now_test<T: ProvidesDaysLength>(
         timestamp_now: TimeProvider<T>,
-        compare_stamp: DateTime<Utc>,
+        compare_stamp: chrono::DateTime<chrono::Utc>,
     ) {
         let dt = timestamp_now.chrono_date_time().unwrap();
         if compare_stamp.year() > dt.year() {
@@ -1591,35 +1615,35 @@ mod tests {
     #[test]
     fn test_time_now() {
         let timestamp_now = TimeProvider::from_now_with_u16_days().unwrap();
-        let compare_stamp = Utc::now();
+        let compare_stamp = chrono::Utc::now();
         generic_now_test(timestamp_now, compare_stamp);
     }
 
     #[test]
     fn test_time_now_us_prec() {
         let timestamp_now = TimeProvider::from_now_with_u16_days_us_precision().unwrap();
-        let compare_stamp = Utc::now();
+        let compare_stamp = chrono::Utc::now();
         generic_now_test(timestamp_now, compare_stamp);
     }
 
     #[test]
     fn test_time_now_ps_prec() {
         let timestamp_now = TimeProvider::from_now_with_u16_days_ps_precision().unwrap();
-        let compare_stamp = Utc::now();
+        let compare_stamp = chrono::Utc::now();
         generic_now_test(timestamp_now, compare_stamp);
     }
 
     #[test]
     fn test_time_now_ps_prec_u16_days() {
         let timestamp_now = TimeProvider::from_now_with_u16_days_ps_precision().unwrap();
-        let compare_stamp = Utc::now();
+        let compare_stamp = chrono::Utc::now();
         generic_now_test(timestamp_now, compare_stamp);
     }
 
     #[test]
     fn test_time_now_ps_prec_u24_days() {
         let timestamp_now = TimeProvider::from_now_with_u24_days_ps_precision().unwrap();
-        let compare_stamp = Utc::now();
+        let compare_stamp = chrono::Utc::now();
         generic_now_test(timestamp_now, compare_stamp);
     }
 
@@ -1743,19 +1767,19 @@ mod tests {
         assert_eq!(stamp_deserialized.submillis(), 5e8 as u32);
     }
 
-    fn generic_dt_case_0_no_prec(subsec_millis: u32) -> DateTime<Utc> {
+    fn generic_dt_case_0_no_prec(subsec_millis: u32) -> chrono::DateTime<chrono::Utc> {
         NaiveDate::from_ymd_opt(2023, 1, 14)
             .unwrap()
             .and_hms_milli_opt(16, 49, 30, subsec_millis)
             .unwrap()
-            .and_local_timezone(Utc)
+            .and_local_timezone(chrono::Utc)
             .unwrap()
     }
 
     fn generic_check_dt_case_0<DaysLen: ProvidesDaysLength>(
         time_provider: &TimeProvider<DaysLen>,
         subsec_millis: u32,
-        datetime_utc: DateTime<Utc>,
+        datetime_utc: chrono::DateTime<chrono::Utc>,
     ) {
         // https://www.timeanddate.com/date/durationresult.html?d1=01&m1=01&y1=1958&d2=14&m2=01&y2=2023
         // Leap years need to be accounted for as well.
@@ -1790,21 +1814,21 @@ mod tests {
         assert_eq!(time_provider, time_provider_2);
     }
 
-    fn generic_dt_case_1_us_prec(subsec_millis: u32) -> DateTime<Utc> {
+    fn generic_dt_case_1_us_prec(subsec_millis: u32) -> chrono::DateTime<chrono::Utc> {
         // 250 ms + 500 us
         let subsec_micros = subsec_millis * 1000 + 500;
         NaiveDate::from_ymd_opt(2023, 1, 14)
             .unwrap()
             .and_hms_micro_opt(16, 49, 30, subsec_micros)
             .unwrap()
-            .and_local_timezone(Utc)
+            .and_local_timezone(chrono::Utc)
             .unwrap()
     }
 
     fn generic_check_dt_case_1_us_prec<DaysLen: ProvidesDaysLength>(
         time_provider: &TimeProvider<DaysLen>,
         subsec_millis: u32,
-        datetime_utc: DateTime<Utc>,
+        datetime_utc: chrono::DateTime<chrono::Utc>,
     ) {
         // https://www.timeanddate.com/date/durationresult.html?d1=01&m1=01&y1=1958&d2=14&m2=01&y2=2023
         // Leap years need to be accounted for as well.
@@ -1839,7 +1863,7 @@ mod tests {
         generic_check_dt_case_1_us_prec(&time_provider, subsec_millis, datetime_utc);
     }
 
-    fn generic_dt_case_2_ps_prec(subsec_millis: u32) -> (DateTime<Utc>, u32) {
+    fn generic_dt_case_2_ps_prec(subsec_millis: u32) -> (chrono::DateTime<chrono::Utc>, u32) {
         // 250 ms + 500 us
         let subsec_nanos = subsec_millis * 1000 * 1000 + 500 * 1000;
         let submilli_nanos = subsec_nanos % 10_u32.pow(6);
@@ -1848,7 +1872,7 @@ mod tests {
                 .unwrap()
                 .and_hms_nano_opt(16, 49, 30, subsec_nanos)
                 .unwrap()
-                .and_local_timezone(Utc)
+                .and_local_timezone(chrono::Utc)
                 .unwrap(),
             submilli_nanos,
         )
@@ -1858,7 +1882,7 @@ mod tests {
         time_provider: &TimeProvider<DaysLen>,
         subsec_millis: u32,
         submilli_nanos: u32,
-        datetime_utc: DateTime<Utc>,
+        datetime_utc: chrono::DateTime<chrono::Utc>,
     ) {
         // https://www.timeanddate.com/date/durationresult.html?d1=01&m1=01&y1=1958&d2=14&m2=01&y2=2023
         // Leap years need to be accounted for as well.
@@ -1907,10 +1931,10 @@ mod tests {
     fn test_creation_from_unix_stamp_0_u16_days() {
         let unix_secs = 0;
         let subsec_millis = 0;
-        let time_provider = TimeProvider::from_unix_secs_with_u16_days(&UnixTimestamp::const_new(
-            unix_secs,
-            subsec_millis,
-        ))
+        let time_provider = TimeProvider::from_unix_stamp_with_u16_days(
+            &UnixTimestamp::new(unix_secs, subsec_millis),
+            SubmillisPrecision::Absent,
+        )
         .expect("creating provider from unix stamp failed");
         assert_eq!(time_provider.ccsds_days, -DAYS_CCSDS_TO_UNIX as u16)
     }
@@ -1919,10 +1943,10 @@ mod tests {
     fn test_creation_from_unix_stamp_0_u24_days() {
         let unix_secs = 0;
         let subsec_millis = 0;
-        let time_provider = TimeProvider::from_unix_secs_with_u24_days(&UnixTimestamp::const_new(
-            unix_secs,
-            subsec_millis,
-        ))
+        let time_provider = TimeProvider::from_unix_stamp_with_u24_days(
+            &UnixTimestamp::new(unix_secs, subsec_millis),
+            SubmillisPrecision::Absent,
+        )
         .expect("creating provider from unix stamp failed");
         assert_eq!(time_provider.ccsds_days, (-DAYS_CCSDS_TO_UNIX) as u32)
     }
@@ -1934,10 +1958,13 @@ mod tests {
             .unwrap()
             .and_hms_milli_opt(16, 49, 30, subsec_millis)
             .unwrap()
-            .and_local_timezone(Utc)
+            .and_local_timezone(chrono::Utc)
             .unwrap();
-        let time_provider = TimeProvider::from_unix_secs_with_u16_days(&datetime_utc.into())
-            .expect("creating provider from unix stamp failed");
+        let time_provider = TimeProvider::from_unix_stamp_with_u16_days(
+            &datetime_utc.into(),
+            SubmillisPrecision::Absent,
+        )
+        .expect("creating provider from unix stamp failed");
         // https://www.timeanddate.com/date/durationresult.html?d1=01&m1=01&y1=1958&d2=14&m2=01&y2=2023
         // Leap years need to be accounted for as well.
         assert_eq!(time_provider.ccsds_days, 23754);
@@ -1953,10 +1980,10 @@ mod tests {
     fn test_creation_0_ccsds_days() {
         let unix_secs = DAYS_CCSDS_TO_UNIX as i64 * SECONDS_PER_DAY as i64;
         let subsec_millis = 0;
-        let time_provider = TimeProvider::from_unix_secs_with_u16_days(&UnixTimestamp::const_new(
-            unix_secs,
-            subsec_millis,
-        ))
+        let time_provider = TimeProvider::from_unix_stamp_with_u16_days(
+            &UnixTimestamp::new(unix_secs, subsec_millis),
+            SubmillisPrecision::Absent,
+        )
         .expect("creating provider from unix stamp failed");
         assert_eq!(time_provider.ccsds_days, 0)
     }
@@ -1965,10 +1992,10 @@ mod tests {
     fn test_invalid_creation_from_unix_stamp_days_too_large() {
         let invalid_unix_secs: i64 = (u16::MAX as i64 + 1) * SECONDS_PER_DAY as i64;
         let subsec_millis = 0;
-        match TimeProvider::from_unix_secs_with_u16_days(&UnixTimestamp::const_new(
-            invalid_unix_secs,
-            subsec_millis,
-        )) {
+        match TimeProvider::from_unix_stamp_with_u16_days(
+            &UnixTimestamp::new(invalid_unix_secs, subsec_millis),
+            SubmillisPrecision::Absent,
+        ) {
             Ok(_) => {
                 panic!("creation should not succeed")
             }
@@ -1992,21 +2019,26 @@ mod tests {
         // precisely 31-12-1957 23:59:55
         let unix_secs = DAYS_CCSDS_TO_UNIX * SECONDS_PER_DAY as i32 - 5;
         let subsec_millis = 0;
-        match TimeProvider::from_unix_secs_with_u16_days(&UnixTimestamp::const_new(
-            unix_secs as i64,
-            subsec_millis,
-        )) {
+        match TimeProvider::from_unix_stamp_with_u16_days(
+            &UnixTimestamp::new(unix_secs as i64, subsec_millis),
+            SubmillisPrecision::Absent,
+        ) {
             Ok(_) => {
                 panic!("creation should not succeed")
             }
             Err(e) => {
                 if let TimestampError::DateBeforeCcsdsEpoch(dt) = e {
-                    assert_eq!(dt.year(), 1957);
-                    assert_eq!(dt.month(), 12);
-                    assert_eq!(dt.day(), 31);
-                    assert_eq!(dt.hour(), 23);
-                    assert_eq!(dt.minute(), 59);
-                    assert_eq!(dt.second(), 55);
+                    let dt = dt.as_date_time();
+                    if let chrono::LocalResult::Single(dt) = dt {
+                        assert_eq!(dt.year(), 1957);
+                        assert_eq!(dt.month(), 12);
+                        assert_eq!(dt.day(), 31);
+                        assert_eq!(dt.hour(), 23);
+                        assert_eq!(dt.minute(), 59);
+                        assert_eq!(dt.second(), 55);
+                    } else {
+                        panic!("unexpected error {}", e)
+                    }
                 } else {
                     panic!("unexpected error {}", e)
                 }
@@ -2222,12 +2254,12 @@ mod tests {
             .unwrap()
             .and_hms_milli_opt(23, 59, 59, 999)
             .unwrap()
-            .and_local_timezone(Utc)
+            .and_local_timezone(chrono::Utc)
             .unwrap();
         let time_provider = TimeProvider::from_dt_with_u24_days(&datetime_utc);
         assert!(time_provider.is_err());
         if let TimestampError::DateBeforeCcsdsEpoch(dt) = time_provider.unwrap_err() {
-            assert_eq!(dt, datetime_utc);
+            assert_eq!(dt, datetime_utc.into());
         }
     }
 
diff --git a/src/time/cuc.rs b/src/time/cuc.rs
index 382ec84..db855e5 100644
--- a/src/time/cuc.rs
+++ b/src/time/cuc.rs
@@ -2,15 +2,29 @@
 //! [CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf) section 3.2 .
 //!
 //! The core data structure to do this is the [TimeProviderCcsdsEpoch] struct.
-use super::*;
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+
+use core::fmt::{Debug, Display, Formatter};
+use core::ops::{Add, AddAssign};
+use core::time::Duration;
+use core::u64;
+
+use crate::ByteConversionError;
+
+use super::{CcsdsTimeCodes, TimestampError, unix_epoch_to_ccsds_epoch, UnixTimestamp, ccsds_epoch_to_unix_epoch, TimeReader, TimeWriter, CcsdsTimeProvider};
+#[cfg(feature = "std")]
+use super::StdTimestampError;
+#[cfg(feature = "std")]
+use std::error::Error;
+#[cfg(feature = "std")]
+use std::time::SystemTime;
 
 #[cfg(feature = "chrono")]
 use chrono::Datelike;
 
-use core::fmt::Debug;
-use core::ops::{Add, AddAssign};
-use core::time::Duration;
-use core::u64;
+#[cfg(feature = "alloc")]
+use super::ccsds_time_code_from_p_field;
 
 const MIN_CUC_LEN: usize = 2;
 
@@ -301,6 +315,7 @@ impl TimeProviderCcsdsEpoch {
     #[cfg(feature = "std")]
     #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
     pub fn update_from_now(&mut self) -> Result<(), StdTimestampError> {
+
         let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)?;
         self.counter.1 = unix_epoch_to_ccsds_epoch(now.as_secs() as i64) as u32;
         self.counter
@@ -325,7 +340,9 @@ impl TimeProviderCcsdsEpoch {
     ) -> Result<Self, TimestampError> {
         // Year before CCSDS epoch is invalid.
         if dt.year() < 1958 {
-            return Err(TimestampError::DateBeforeCcsdsEpoch(*dt));
+            return Err(TimestampError::DateBeforeCcsdsEpoch(UnixTimestamp::from(
+                *dt,
+            )));
         }
         let counter = dt
             .timestamp()
@@ -349,9 +366,7 @@ impl TimeProviderCcsdsEpoch {
         let ccsds_epoch = unix_epoch_to_ccsds_epoch(unix_stamp.unix_seconds);
         // Negative CCSDS epoch is invalid.
         if ccsds_epoch < 0 {
-            return Err(TimestampError::DateBeforeCcsdsEpoch(
-                unix_stamp.as_date_time().unwrap(),
-            ));
+            return Err(TimestampError::DateBeforeCcsdsEpoch(*unix_stamp));
         }
         ccsds_epoch
             .checked_add(i64::from(leap_seconds))
@@ -682,43 +697,16 @@ impl CcsdsTimeProvider for TimeProviderCcsdsEpoch {
         self.unix_seconds()
     }
 
-    fn subsecond_millis(&self) -> u16 {
+    fn subsecond_nanos(&self) -> u32 {
         if let Some(fractions) = self.fractions {
             if fractions.0 == FractionalResolution::Seconds {
                 return 0;
             }
             // Rounding down here is the correct approach.
-            return (convert_fractional_part_to_ns(fractions) / 10_u32.pow(6) as u64) as u16;
+            return convert_fractional_part_to_ns(fractions) as u32;
         }
         0
     }
-
-    #[cfg(feature = "chrono")]
-    #[cfg_attr(doc_cfg, doc(cfg(feature = "chrono")))]
-    fn chrono_date_time(&self) -> Option<chrono::DateTime<chrono::Utc>> {
-        let mut ns = 0;
-        if let Some(fractional_part) = self.fractions {
-            ns = convert_fractional_part_to_ns(fractional_part);
-        }
-        if let LocalResult::Single(res) = chrono::Utc.timestamp_opt(self.unix_seconds(), ns as u32)
-        {
-            return Some(res);
-        }
-        None
-    }
-
-    #[cfg(feature = "timelib")]
-    #[cfg_attr(doc_cfg, doc(cfg(feature = "timelib")))]
-    fn timelib_date_time(&self) -> Result<time::OffsetDateTime, time::error::ComponentRange> {
-        let mut ns = 0;
-        if let Some(fractional_part) = self.fractions {
-            ns = convert_fractional_part_to_ns(fractional_part);
-        }
-        Ok(
-            time::OffsetDateTime::from_unix_timestamp(self.unix_seconds())?
-                + time::Duration::nanoseconds(ns as i64),
-        )
-    }
 }
 
 fn get_provider_values_after_duration_addition(
@@ -818,9 +806,11 @@ impl Add<Duration> for &TimeProviderCcsdsEpoch {
 
 #[cfg(test)]
 mod tests {
+    use crate::time::{UnixTimestamp, DAYS_CCSDS_TO_UNIX, SECONDS_PER_DAY};
+
     use super::*;
     use alloc::string::ToString;
-    use chrono::{Datelike, Timelike};
+    use chrono::{Datelike, TimeZone, Timelike};
     #[allow(unused_imports)]
     use std::println;
 
@@ -840,14 +830,14 @@ mod tests {
         let fractions = zero_cuc.width_fractions_pair();
         assert!(fractions.is_none());
         let dt = zero_cuc.chrono_date_time();
-        assert!(dt.is_some());
-        let dt = dt.unwrap();
-        assert_eq!(dt.year(), 1958);
-        assert_eq!(dt.month(), 1);
-        assert_eq!(dt.day(), 1);
-        assert_eq!(dt.hour(), 0);
-        assert_eq!(dt.minute(), 0);
-        assert_eq!(dt.second(), 0);
+        if let chrono::LocalResult::Single(dt) = dt {
+            assert_eq!(dt.year(), 1958);
+            assert_eq!(dt.month(), 1);
+            assert_eq!(dt.day(), 1);
+            assert_eq!(dt.hour(), 0);
+            assert_eq!(dt.minute(), 0);
+            assert_eq!(dt.second(), 0);
+        }
     }
 
     #[test]
@@ -862,7 +852,7 @@ mod tests {
         let zero_cuc = zero_cuc.unwrap();
         let res = zero_cuc.write_to_bytes(&mut buf);
         assert!(res.is_ok());
-        assert_eq!(zero_cuc.subsecond_millis(), 0);
+        assert_eq!(zero_cuc.subsecond_nanos(), 0);
         assert_eq!(zero_cuc.len_as_bytes(), 5);
         assert_eq!(pfield_len(buf[0]), 1);
         let written = res.unwrap();
@@ -880,17 +870,19 @@ mod tests {
 
     #[test]
     fn test_datetime_now() {
-        let now = Utc::now();
+        let now = chrono::Utc::now();
         let cuc_now = TimeProviderCcsdsEpoch::from_now(FractionalResolution::SixtyNs, LEAP_SECONDS);
         assert!(cuc_now.is_ok());
         let cuc_now = cuc_now.unwrap();
         let dt_opt = cuc_now.chrono_date_time();
-        assert!(dt_opt.is_some());
-        let dt = dt_opt.unwrap();
-        let diff = dt - now;
-        assert!(diff.num_milliseconds() < 1000);
-        println!("datetime from cuc: {}", dt);
-        println!("datetime now: {}", now);
+        if let chrono::LocalResult::Single(dt) = dt_opt {
+            let diff = dt - now;
+            assert!(diff.num_milliseconds() < 1000);
+            println!("datetime from cuc: {}", dt);
+            println!("datetime now: {}", now);
+        } else {
+            panic!("date time creation from now failed")
+        }
     }
 
     #[test]
@@ -1316,7 +1308,7 @@ mod tests {
 
     #[test]
     fn test_from_dt() {
-        let dt = Utc.with_ymd_and_hms(2021, 1, 1, 0, 0, 0).unwrap();
+        let dt = chrono::Utc.with_ymd_and_hms(2021, 1, 1, 0, 0, 0).unwrap();
         let cuc = TimeProviderCcsdsEpoch::from_chrono_date_time(
             &dt,
             FractionalResolution::Seconds,
@@ -1335,7 +1327,7 @@ mod tests {
 
     #[test]
     fn from_unix_stamp() {
-        let unix_stamp = UnixTimestamp::new(0, 0).unwrap();
+        let unix_stamp = UnixTimestamp::new(0, 0);
         let cuc = TimeProviderCcsdsEpoch::from_unix_stamp(
             &unix_stamp,
             FractionalResolution::Seconds,
diff --git a/src/time/mod.rs b/src/time/mod.rs
index c5d4734..004772d 100644
--- a/src/time/mod.rs
+++ b/src/time/mod.rs
@@ -1,5 +1,6 @@
 //! CCSDS Time Code Formats according to [CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
 use crate::ByteConversionError;
+#[cfg(feature = "chrono")]
 use chrono::{DateTime, LocalResult, TimeZone, Utc};
 use core::cmp::Ordering;
 use core::fmt::{Display, Formatter};
@@ -13,6 +14,7 @@ use num_traits::float::FloatCore;
 
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
+
 #[cfg(feature = "std")]
 use std::error::Error;
 #[cfg(feature = "std")]
@@ -68,7 +70,7 @@ pub enum TimestampError {
     ByteConversion(ByteConversionError),
     Cds(cds::CdsError),
     Cuc(cuc::CucError),
-    DateBeforeCcsdsEpoch(DateTime<Utc>),
+    DateBeforeCcsdsEpoch(UnixTimestamp),
     CustomEpochNotSupported,
 }
 
@@ -91,7 +93,7 @@ impl Display for TimestampError {
                 write!(f, "time stamp: {e}")
             }
             TimestampError::DateBeforeCcsdsEpoch(e) => {
-                write!(f, "datetime with date before ccsds epoch: {e}")
+                write!(f, "datetime with date before ccsds epoch: {e:?}")
             }
             TimestampError::CustomEpochNotSupported => {
                 write!(f, "custom epochs are not supported")
@@ -231,59 +233,101 @@ pub trait CcsdsTimeProvider {
     fn ccdsd_time_code(&self) -> CcsdsTimeCodes;
 
     fn unix_seconds(&self) -> i64;
-    fn subsecond_millis(&self) -> u16;
+    fn subsecond_nanos(&self) -> u32;
+
+    fn subsecond_millis(&self) -> u16 {
+        (self.subsecond_nanos() / 1_000_000) as u16
+    }
+
     fn unix_stamp(&self) -> UnixTimestamp {
-        UnixTimestamp::const_new(self.unix_seconds(), self.subsecond_millis())
+        UnixTimestamp::new(self.unix_seconds(), self.subsecond_nanos())
     }
 
     #[cfg(feature = "chrono")]
     #[cfg_attr(doc_cfg, doc(cfg(feature = "chrono")))]
-    fn chrono_date_time(&self) -> Option<chrono::DateTime<chrono::Utc>>;
+    fn chrono_date_time(&self) -> chrono::LocalResult<chrono::DateTime<chrono::Utc>> {
+        chrono::Utc.timestamp_opt(self.unix_seconds(), self.subsecond_nanos())
+    }
 
     #[cfg(feature = "timelib")]
     #[cfg_attr(doc_cfg, doc(cfg(feature = "timelib")))]
-    fn timelib_date_time(&self) -> Result<time::OffsetDateTime, time::error::ComponentRange>;
+    fn timelib_date_time(&self) -> Result<time::OffsetDateTime, time::error::ComponentRange> {
+        Ok(
+            time::OffsetDateTime::from_unix_timestamp(self.unix_seconds())?
+                + time::Duration::nanoseconds(self.subsecond_nanos().into()),
+        )
+    }
 }
 
 /// UNIX timestamp: Elapsed seconds since 1970-01-01T00:00:00+00:00.
 ///
 /// Also can optionally include subsecond millisecond for greater accuracy.
+/// It is assumed that leap second correction was already applied and the reference time is UTC.
 #[derive(Default, Debug, Copy, Clone, PartialEq, Eq)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct UnixTimestamp {
     pub unix_seconds: i64,
-    subsecond_millis: u16,
+    subsecond_nanos: u32,
 }
 
 impl UnixTimestamp {
-    /// Returns [None] if the subsecond millisecond value is larger than 999.
-    pub fn new(unix_seconds: i64, subsec_millis: u16) -> Option<Self> {
+    /// Returns [None] if the subsecond nanosecond value is invalid (larger than fraction of a
+    /// second)
+    pub fn new_checked(unix_seconds: i64, subsec_nanos: u32) -> Option<Self> {
+        if subsec_nanos > 1_000_000_000 - 1 {
+            return None;
+        }
+        Some(Self::new(unix_seconds, subsec_nanos))
+    }
+
+    /// Returns [None] if the subsecond millisecond value is invalid (larger than fraction of a
+    /// second)
+    pub fn new_subsec_millis_checked(unix_seconds: i64, subsec_millis: u16) -> Option<Self> {
         if subsec_millis > 999 {
             return None;
         }
-        Some(Self::const_new(unix_seconds, subsec_millis))
+        Self::new_checked(unix_seconds, subsec_millis as u32 * 1_000_000)
     }
 
-    /// Like [Self::new] but const. Panics if the subsecond value is larger than 999.
-    pub const fn const_new(unix_seconds: i64, subsecond_millis: u16) -> Self {
-        if subsecond_millis > 999 {
-            panic!("subsec milliseconds exceeds 999");
+    /// This function will panic if the subsecond value is larger than the fraction of a second.
+    /// Use [new_checked] if you want to handle this case without a panic.
+    pub const fn new(unix_seconds: i64, subsecond_nanos: u32) -> Self {
+        // This could actually be used to model leap seconds, but we will ignore that for now.
+        if subsecond_nanos > 1_000_000_000 - 1 {
+            panic!("invalid subsecond nanos value");
         }
         Self {
             unix_seconds,
-            subsecond_millis,
+            subsecond_nanos,
+        }
+    }
+
+    /// This function will panic if the subsecond value is larger than the fraction of a second.
+    /// Use [new_subsecond_millis_checked] if you want to handle this case without a panic.
+    pub const fn new_subsec_millis(unix_seconds: i64, subsecond_millis: u16) -> Self {
+        // This could actually be used to model leap seconds, but we will ignore that for now.
+        if subsecond_millis > 999 {
+            panic!("invalid subsecond millisecond value");
+        }
+        Self {
+            unix_seconds,
+            subsecond_nanos: subsecond_millis as u32 * 1_000_000,
         }
     }
 
     pub fn new_only_seconds(unix_seconds: i64) -> Self {
         Self {
             unix_seconds,
-            subsecond_millis: 0,
+            subsecond_nanos: 0,
         }
     }
 
     pub fn subsecond_millis(&self) -> u16 {
-        self.subsecond_millis
+        (self.subsecond_nanos / 1_000_000) as u16
+    }
+
+    pub fn subsecond_nanos(&self) -> u32 {
+        self.subsecond_nanos
     }
 
     #[cfg(feature = "std")]
@@ -291,19 +335,16 @@ impl UnixTimestamp {
     pub fn from_now() -> Result<Self, SystemTimeError> {
         let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)?;
         let epoch = now.as_secs();
-        Ok(Self::const_new(epoch as i64, now.subsec_millis() as u16))
+        Ok(Self::new(epoch as i64, now.subsec_nanos()))
     }
 
     #[inline]
     pub fn unix_seconds_f64(&self) -> f64 {
-        self.unix_seconds as f64 + (self.subsecond_millis as f64 / 1000.0)
+        self.unix_seconds as f64 + (self.subsecond_nanos as f64 / 1_000_000_000.0)
     }
 
     pub fn as_date_time(&self) -> LocalResult<DateTime<Utc>> {
-        Utc.timestamp_opt(
-            self.unix_seconds,
-            self.subsecond_millis as u32 * 10_u32.pow(6),
-        )
+        Utc.timestamp_opt(self.unix_seconds, self.subsecond_nanos)
     }
 
     // Calculate the difference in milliseconds between two UnixTimestamps
@@ -313,16 +354,16 @@ impl UnixTimestamp {
         let milliseconds_difference = seconds_difference * 1000;
 
         // Calculate the difference in subsecond milliseconds directly
-        let subsecond_difference = self.subsecond_millis as i64 - other.subsecond_millis as i64;
+        let subsecond_difference_nanos = self.subsecond_nanos as i64 - other.subsecond_nanos as i64;
 
         // Combine the differences
-        milliseconds_difference + subsecond_difference
+        milliseconds_difference + (subsecond_difference_nanos / 1_000_000)
     }
 }
 
 impl From<DateTime<Utc>> for UnixTimestamp {
     fn from(value: DateTime<Utc>) -> Self {
-        Self::const_new(value.timestamp(), value.timestamp_subsec_millis() as u16)
+        Self::new(value.timestamp(), value.timestamp_subsec_nanos())
     }
 }
 
@@ -395,7 +436,7 @@ fn get_new_stamp_after_addition(
     current_stamp: &UnixTimestamp,
     duration: Duration,
 ) -> UnixTimestamp {
-    let mut new_subsec_millis = current_stamp.subsecond_millis() + duration.subsec_millis() as u16;
+    let mut new_subsec_nanos = current_stamp.subsecond_nanos() + duration.subsec_nanos();
     let mut new_unix_seconds = current_stamp.unix_seconds;
     let mut increment_seconds = |value: u32| {
         if new_unix_seconds < 0 {
@@ -408,8 +449,8 @@ fn get_new_stamp_after_addition(
                 .expect("new unix seconds would exceed i64::MAX");
         }
     };
-    if new_subsec_millis >= 1000 {
-        new_subsec_millis -= 1000;
+    if new_subsec_nanos >= 1_000_000_000 {
+        new_subsec_nanos -= 1_000_000_000;
         increment_seconds(1);
     }
     increment_seconds(
@@ -418,7 +459,7 @@ fn get_new_stamp_after_addition(
             .try_into()
             .expect("duration seconds exceeds u32::MAX"),
     );
-    UnixTimestamp::const_new(new_unix_seconds, new_subsec_millis)
+    UnixTimestamp::new(new_unix_seconds, new_subsec_nanos)
 }
 
 /// Please note that this operation will panic on the following conditions:
@@ -457,10 +498,15 @@ impl Add<Duration> for &UnixTimestamp {
 mod tests {
     use alloc::string::ToString;
     use chrono::{Datelike, Timelike};
-    use std::format;
+    use std::{format, println};
 
     use super::{cuc::CucError, *};
 
+    #[allow(dead_code)]
+    const UNIX_STAMP_CONST: UnixTimestamp = UnixTimestamp::new(5, 999_999_999);
+    #[allow(dead_code)]
+    const UNIX_STAMP_CONST_2: UnixTimestamp = UnixTimestamp::new_subsec_millis(5, 999);
+
     #[test]
     fn test_days_conversion() {
         assert_eq!(unix_to_ccsds_days(DAYS_CCSDS_TO_UNIX.into()), 0);
@@ -506,17 +552,18 @@ mod tests {
 
     #[test]
     fn basic_float_unix_stamp_test() {
-        let stamp = UnixTimestamp::new(500, 600).unwrap();
+        let stamp = UnixTimestamp::new_subsec_millis_checked(500, 600).unwrap();
         assert_eq!(stamp.unix_seconds, 500);
         let subsec_millis = stamp.subsecond_millis();
         assert_eq!(subsec_millis, 600);
+        println!("{:?}", (500.6 - stamp.unix_seconds_f64()).to_string());
         assert!((500.6 - stamp.unix_seconds_f64()).abs() < 0.0001);
     }
 
     #[test]
     fn test_ord_larger() {
         let stamp0 = UnixTimestamp::new_only_seconds(5);
-        let stamp1 = UnixTimestamp::new(5, 500).unwrap();
+        let stamp1 = UnixTimestamp::new_subsec_millis_checked(5, 500).unwrap();
         let stamp2 = UnixTimestamp::new_only_seconds(6);
         assert!(stamp1 > stamp0);
         assert!(stamp2 > stamp0);
@@ -526,7 +573,7 @@ mod tests {
     #[test]
     fn test_ord_smaller() {
         let stamp0 = UnixTimestamp::new_only_seconds(5);
-        let stamp1 = UnixTimestamp::new(5, 500).unwrap();
+        let stamp1 = UnixTimestamp::new_subsec_millis_checked(5, 500).unwrap();
         let stamp2 = UnixTimestamp::new_only_seconds(6);
         assert!(stamp0 < stamp1);
         assert!(stamp0 < stamp2);
@@ -536,7 +583,7 @@ mod tests {
     #[test]
     fn test_ord_larger_neg_numbers() {
         let stamp0 = UnixTimestamp::new_only_seconds(-5);
-        let stamp1 = UnixTimestamp::new(-5, 500).unwrap();
+        let stamp1 = UnixTimestamp::new_subsec_millis_checked(-5, 500).unwrap();
         let stamp2 = UnixTimestamp::new_only_seconds(-6);
         assert!(stamp0 > stamp1);
         assert!(stamp0 > stamp2);
@@ -548,7 +595,7 @@ mod tests {
     #[test]
     fn test_ord_smaller_neg_numbers() {
         let stamp0 = UnixTimestamp::new_only_seconds(-5);
-        let stamp1 = UnixTimestamp::new(-5, 500).unwrap();
+        let stamp1 = UnixTimestamp::new_subsec_millis_checked(-5, 500).unwrap();
         let stamp2 = UnixTimestamp::new_only_seconds(-6);
         assert!(stamp2 < stamp1);
         assert!(stamp2 < stamp0);
@@ -560,7 +607,7 @@ mod tests {
     #[allow(clippy::nonminimal_bool)]
     #[test]
     fn test_eq() {
-        let stamp0 = UnixTimestamp::new(5, 0).unwrap();
+        let stamp0 = UnixTimestamp::new(5, 0);
         let stamp1 = UnixTimestamp::new_only_seconds(5);
         assert_eq!(stamp0, stamp1);
         assert!(stamp0 <= stamp1);
@@ -582,7 +629,7 @@ mod tests {
 
     #[test]
     fn test_addition_on_ref() {
-        let stamp0 = &UnixTimestamp::new(20, 500).unwrap();
+        let stamp0 = &UnixTimestamp::new_subsec_millis_checked(20, 500).unwrap();
         let stamp1 = stamp0 + Duration::from_millis(2500);
         assert_eq!(stamp1.unix_seconds, 23);
         assert_eq!(stamp1.subsecond_millis(), 0);
@@ -609,19 +656,19 @@ mod tests {
 
     #[test]
     fn test_stamp_diff_positive_0() {
-        let stamp_later = UnixTimestamp::new(2, 0).unwrap();
+        let stamp_later = UnixTimestamp::new(2, 0);
         let StampDiff {
             positive_duration,
             duration_absolute,
-        } = stamp_later - UnixTimestamp::new(1, 0).unwrap();
+        } = stamp_later - UnixTimestamp::new(1, 0);
         assert!(positive_duration);
         assert_eq!(duration_absolute, Duration::from_secs(1));
     }
 
     #[test]
     fn test_stamp_diff_positive_1() {
-        let stamp_later = UnixTimestamp::new(3, 800).unwrap();
-        let stamp_earlier = UnixTimestamp::new(1, 900).unwrap();
+        let stamp_later = UnixTimestamp::new(3, 800 * 1_000_000);
+        let stamp_earlier = UnixTimestamp::new_subsec_millis_checked(1, 900).unwrap();
         let StampDiff {
             positive_duration,
             duration_absolute,
@@ -632,8 +679,8 @@ mod tests {
 
     #[test]
     fn test_stamp_diff_negative() {
-        let stamp_later = UnixTimestamp::new(3, 800).unwrap();
-        let stamp_earlier = UnixTimestamp::new(1, 900).unwrap();
+        let stamp_later = UnixTimestamp::new_subsec_millis_checked(3, 800).unwrap();
+        let stamp_earlier = UnixTimestamp::new_subsec_millis_checked(1, 900).unwrap();
         let StampDiff {
             positive_duration,
             duration_absolute,
@@ -644,7 +691,7 @@ mod tests {
 
     #[test]
     fn test_addition_spillover() {
-        let mut stamp0 = UnixTimestamp::new(1, 900).unwrap();
+        let mut stamp0 = UnixTimestamp::new_subsec_millis_checked(1, 900).unwrap();
         stamp0 += Duration::from_millis(100);
         assert_eq!(stamp0.unix_seconds, 2);
         assert_eq!(stamp0.subsecond_millis(), 0);