Calculating time that goes past Midnight

In the attachment, I show a timesheet with a drop down to select time of day. I cannot just use an equation that subtracts time, because night shift begins at 7pm or 11pm and works past midnight into the next day. Any idea how to make my drop downs in such a way that 7pm to 7am = 12 Hours? Thank you very much to anyone who can help!

If you have start time in A2 and end time in B2 this will give you the duration whether the shift passes midnight or not

=MOD(B2-A2,1)

format result cell in time format

that will give you 12:00 for you example, if you want 12 multiply by 24, i.e.

=MOD(B2-A2,1)*24

format as number

Wow...that was WAY simpler than what I was trying to do. Thank you!