Time Span in hours

Trying to figure out the hours between two times. Say, for instance, I have 7:00 PM in cell A1 and 6:00 AM in cell A2. What is my formula in cell A3 to give me the result of 11 hours, the hour time span between A1 and A2?

Thank You

Maybe

=MOD(B1-A1,1)

or

=B1-A1+(A1>B1)

VBA Noob