Since we can't calculate time...(yet)<-----hint, hint 
I'm trying to write an IF formula to determine hours. I have a Shift Start (Dropdown List) column, a Shift End (Dropdown List) column, and a Total Hours (Text/Number) column. The dropdown values are listed below. Is this doable? Here's what I'm starting with:
=IF(AND([Shift Start]1 = "4:00AM", [Shift End]1 = "4:15AM"), 0.25, 0)
4:00AM
4:15AM
4:30AM
4:45AM
5:00AM
5:15AM
5:30AM
5:45AM
6:00AM
6:15AM
6:30AM
6:45AM
7:00AM
7:15AM
7:30AM
7:45AM
8:00AM
8:15AM
8:30AM
8:45AM
9:00AM
9:15AM
9:30AM
9:45AM
10:00AM
10:15AM
10:30AM
10:45AM
11:00AM
11:15AM
11:30AM
11:45AM
12:00PM
12:15PM
12:30PM
12:45PM
1:00PM
1:15PM
1:30PM
1:45PM
2:00PM
2:15PM
2:30PM
2:45PM
3:00PM
3:15PM
3:30PM
3:45PM
4:00PM
4:15PM
4:30PM
4:45PM
5:00PM
5:15PM
5:30PM
5:45PM
6:00PM
6:15PM
6:30PM
6:45PM
7:00PM
7:15PM
7:30PM
7:45PM
8:00PM
8:15PM
8:30PM
8:45PM
9:00PM
9:15PM
9:30PM
9:45PM
10:00PM
10:15PM
10:30PM
10:45PM
11:00PM
11:15PM
11:30PM
11:45PM
12:00AM