Counting Time

I am trying to figure out a way to count the number of hours that the PCA is working while the supervisor is working. Is there a formula that will tell me how many hours they are overlapping?

Example:

Supervisor works 8:00 AM-5:00 PM
PCA works 7:00 AM-4:00 PM

I want to know that they are overlapping 8 hours of their day.

if you use military time (i.e. 6PM = 18, 6AM = 6)

Cell A1 = Supervisor Start time
Cell B1 = Supervisor End time

Cell A2 = PCA Start time
Cell B2 = PCA End time

The formula to find the overlap would be as follows:
=MIN(B1:B2)-MAX(A1:A2)

.....although you might want to tweak that slightly to avoid a negative value if there is no overlap, i.e.

=MAX(0,MIN(B1:B2)-MAX(A1:A2))

The time format used shouldn't matter as long as it's recognised by Excel as a time.

Do you have any shift which start one day and end the next, e.g. 23:00 to 07:00?