I'm trying to find out the difference between two times, for example,

In at 20:55 (8:55 PM)
Out at 21:10 (9:10 PM)

I know that if I substract 21:10 from 20:55 I'll get 0:15 minutes.

But my problem is this

In at 23:50 (11:50 PM)
Out at 0:10 (12:10 AM)

I get ###### as my answer, does anybody know how to do this operation??