How to format TimeSpan in XAML

Question

I am trying to format a textblock which is bound to a TimeSpan property. It works if the property is of type DateTime but it fails if it is a

Answer 1

In .NET 3.5 you could use a MultiBinding instead

Update
To answer the comments.

To make sure you output 2 digits even if hours or minutes is 0-9 you can use {0:00} instead of {0}. This will make sure the output for the time 12:01 is 12:01 instead of 12:1.
If you want to output 01:01 as 1:01 use StringFormat="{}{0}:{1:00}"

And Conditional formatting can be used to remove the negative sign for minutes. Instead of {1:00} we can use {1:00;00}