diff --git a/Cargo.toml b/Cargo.toml
index 20017a4..1bf3231 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -29,6 +29,6 @@ version = "0.7.3"
 features = ["use-std"]
 
 [features]
-
+std = ["postcard/use-std"]
 default = ["heapless", "alloc"]
 alloc = ["serde/alloc"]
diff --git a/src/lib.rs b/src/lib.rs
index cf9eb94..7be3cca 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,17 +2,20 @@
 #![no_std]
 extern crate alloc;
 
+#[cfg(feature = "std")]
+extern crate std;
+
 use crate::ecss::CCSDS_HEADER_LEN;
 use serde::{Deserialize, Serialize};
 
 pub mod ecss;
-pub mod time;
 pub mod tc;
+pub mod time;
 pub mod tm;
 
 #[derive(Debug, Copy, Clone, PartialEq)]
 pub enum PacketError {
-    /// The passed slice is too small. Returns the required size of the failed size chgeck
+    /// The passed slice is too small. Returns the required size of the failed size check
     ToBytesSliceTooSmall(usize),
     /// The [zerocopy] library failed to write to bytes
     ToBytesZeroCopyError,
diff --git a/src/time.rs b/src/time.rs
index f8a17ec..1ede74d 100644
--- a/src/time.rs
+++ b/src/time.rs
@@ -1,39 +1,120 @@
-enum CcsdsTimeCodes {
+use crate::PacketError;
+#[cfg(feature = "std")]
+use std::time::SystemTime;
+
+pub const CDS_SHORT_LEN: usize = 7;
+pub const DAYS_CCSDS_TO_UNIX: i32 = -4383;
+pub const SECONDS_PER_DAY: u32 = 86400;
+
+pub enum CcsdsTimeCodes {
     None = 0,
     CucCcsdsEpoch = 0b001,
     CucAgencyEpoch = 0b010,
     Cds = 0b100,
-    Ccs = 0b101
+    Ccs = 0b101,
+}
+
+#[cfg(feature = "std")]
+pub fn seconds_since_epoch() -> f64 {
+    SystemTime::now()
+        .duration_since(SystemTime::UNIX_EPOCH)
+        .expect("System time generation failed")
+        .as_secs_f64()
+}
+
+/// Convert UNIX days to CCSDS days
+///
+///  - CCSDS epoch: 1958 January 1
+///  - UNIX Epoch: 1970 January 1
+pub const fn unix_to_ccsds_days(unix_days: i32) -> i32 {
+    unix_days - DAYS_CCSDS_TO_UNIX
+}
+
+/// Convert CCSDS days to UNIX days
+///
+///  - CCSDS epoch: 1958 January 1
+///  - UNIX Epoch: 1970 January 1
+pub const fn ccsds_to_unix_days(unix_days: i32) -> i32 {
+    unix_days + DAYS_CCSDS_TO_UNIX
 }
 
 /// Trait for generic CCSDS time providers
 trait CcsdsTimeProvider {
-    fn write_to_bytes(&self, bytes: impl AsMut<u8>);
+    fn len(&self) -> usize;
+    fn write_to_bytes(&self, bytes: &mut (impl AsMut<[u8]> + ?Sized)) -> Result<(), PacketError>;
     /// Returns the pfield of the time provider. The pfield can have one or two bytes depending
     /// on the extension bit (first bit). The time provider should returns a tuple where the first
     /// entry denotes the length of the pfield and the second entry is the value of the pfield
     /// in big endian format.
-    fn pfield(&self) -> (usize, u16);
+    fn p_field(&self) -> (usize, [u8; 2]);
     fn ccdsd_time_code(&self) -> CcsdsTimeCodes;
     fn as_unix_seconds(&self) -> u64;
 }
 
-struct CdsShortTimeProvider {}
+pub struct CdsShortTimeProvider {
+    pfield: u8,
+    ccsds_days: u16,
+    ms_of_day: u32,
+    unix_seconds: u64,
+}
 
-impl CcsdsTimeProvider for CdsShortTimeProvider {
-    fn write_to_bytes(&self, bytes: impl AsMut<u8>) {
-        todo!()
+impl CdsShortTimeProvider {
+    pub fn new(ccsds_days: u16, ms_of_day: u32) -> Self {
+        let mut provider = Self {
+            pfield: (CcsdsTimeCodes::Cds as u8) << 4,
+            ccsds_days,
+            ms_of_day,
+            unix_seconds: 0,
+        };
+        provider.calc_unix_seconds();
+        provider
     }
 
-    fn pfield(&self) -> (usize, u16) {
-        todo!()
+    #[cfg(feature = "std")]
+    pub fn ms_of_day_using_sysclock() -> u32 {
+        Self::ms_of_day(seconds_since_epoch())
+    }
+
+    pub fn ms_of_day(seconds_since_epoch: f64) -> u32 {
+        let fraction_ms = seconds_since_epoch - seconds_since_epoch.floor();
+        let ms_of_day: u32 =
+            (((seconds_since_epoch.floor() as u32 % SECONDS_PER_DAY) * 1000) as f64 + fraction_ms)
+                .floor() as u32;
+        ms_of_day
+    }
+
+    fn calc_unix_seconds(&mut self) {
+        let unix_days = ccsds_to_unix_days(self.ccsds_days as i32);
+        self.unix_seconds = unix_days as u64 * (24 * 60 * 60);
+        let seconds_of_day = (self.ms_of_day as f32 / 1000.0).floor() as u64;
+        self.unix_seconds += seconds_of_day;
+    }
+}
+impl CcsdsTimeProvider for CdsShortTimeProvider {
+    fn len(&self) -> usize {
+        CDS_SHORT_LEN
+    }
+
+    fn write_to_bytes(&self, bytes: &mut (impl AsMut<[u8]> + ?Sized)) -> Result<(), PacketError> {
+        let slice = bytes.as_mut();
+        if slice.len() < self.len() {
+            return Err(PacketError::ToBytesSliceTooSmall(slice.len()));
+        }
+        slice[0] = self.pfield;
+        slice[1..3].copy_from_slice(self.ccsds_days.to_be_bytes().as_slice());
+        slice[4..].copy_from_slice(self.ms_of_day.to_be_bytes().as_slice());
+        Ok(())
+    }
+
+    fn p_field(&self) -> (usize, [u8; 2]) {
+        (1, [self.pfield, 0])
     }
 
     fn ccdsd_time_code(&self) -> CcsdsTimeCodes {
-        todo!()
+        CcsdsTimeCodes::Cds
     }
 
     fn as_unix_seconds(&self) -> u64 {
-        todo!()
+        self.unix_seconds
     }
 }