I need help devising a formula to add hours to a schedule. I have everything complete except for the formula to calculate an overnight shift 10:00 pm to 6:00 am. The trick is to combine this formula in the formula's for the other shifts as well, which include 6:00 am to 2:00 pm and 2:00 pm to 10:00 pm. I need to incorporate it all together. I hope someone understands what I'm trying to ask. I can't just separate the formula's because everyone is flexible with their schedule so they work all three shifts.

Thanks for your help guys! :D

a b c
10:00 am 6:00 pm 8:00
10:00 pm 6:00 am 8:00

=B1-A1+(B1<A1)

Format the cells with this formula as [h]:mm

Perhaps this, just to make sure that both time values are there before doing the math:

=IF(ISBLANK(B1),"",B1-A1+(B1<A1)