Added an implementation of From<Time> for Duration.

src/lib.rs

@@ -248,7 +248,7 @@ pub mod num {
     #[cfg(not(feature = "std"))]
     pub use num_traits::float::FloatCore as Float;
 
-    pub use num_traits::{pow, FromPrimitive, Num, One, Saturating, Signed, Zero};
+    pub use num_traits::{pow, AsPrimitive, FromPrimitive, Num, One, Saturating, Signed, Zero};
 
     #[cfg(feature = "bigint-support")]
     pub use num_bigint::{BigInt, BigUint};

src/si/time.rs

@@ -1,5 +1,7 @@
 //! Time (base unit second, s<sup>1</sup>).
 
+use ::lib::time::Duration;
+
 quantity! {
     /// Time (base unit second, s<sup>1</sup>).
     quantity: Time; "time";
@@ -44,3 +46,15 @@ quantity! {
         @year: 3.1536_E7; "a", "year", "years";
     }
 }
+
+impl<U, V> From<Time<U, V>> for Duration
+where
+    U: ::si::Units<V>,
+    V: ::num::Num + ::num::AsPrimitive<f64> + ::Conversion<V>,
+{
+    fn from(t: Time<U, V>) -> Duration {
+        let secs: f64 = t.value.as_();
+        let nanos = (secs * 1e9) as u64 % 1e9 as u64;
+        Duration::new(secs as u64, nanos as u32)
+    }
+}