How to find difference between 2 time strings in HHMMSSmmmuuu format in C#

How to find difference between 2 time strings in HHMMSSmmmuuu format in C#

I have two time strings in HH:MM:SS:mmm:uuu format. How to find the
difference (time span) between them?
string t1="06:37:30:210:111";
string t2="06:38:32:310:222";
I want to find the difference (in terms of time) between t2 and t1 (t2-t1).
How to do this?