I'm not positive that I understand what you are asking, but I believe you just want to change the time format in your bound data?
That's fairly easy - use StringFormat. For example:
<TextBlock x:Name="txt12Hour" Text="{Binding StringFormat={}{0:hh:mm:ss tt}}" />
<TextBlock x:Name="txt24Hour" Text="{Binding StringFormat={}{0:HH:mm:ss}}" />
txt12Hour shows something like 05:17:27 PM
txt24Hour shows something like 17:17:27
Use any of the same formatting rules that you'd use in a ToString() call in code. This applies not only to dates, but numbers, currencies, etc.