Implement the new fields for timestamp.

src/types/object.rs

@@ -299,6 +299,7 @@ pub struct Timestamp<'s> {
     pub end_time: Option<Time<'s>>,
     pub repeater: Option<Repeater>,
     pub warning_delay: Option<WarningDelay>,
+    pub post_blank: Option<&'s str>,
 }
 
 #[derive(Debug, Clone)]
@@ -964,11 +965,15 @@ impl<'s> StandardProperties<'s> for Timestamp<'s> {
     }
 
     fn get_contents<'b>(&'b self) -> Option<&'s str> {
-        todo!()
+        None
     }
 
     fn get_post_blank(&self) -> PostBlank {
-        todo!()
+        self.post_blank
+            .map(|text| text.chars().count())
+            .unwrap_or(0)
+            .try_into()
+            .expect("Too much post-blank to fit into a PostBlank.")
     }
 }