Nested IF Formulas with Times not caclulating correctly

I have several start/end times and need to also calculate the difference in minutes of those times on occasion.


START A END A START B END B
03/01/13 14:25 03/01/13 16:54 03/01/13 16:52 03/01/13 16:59
03/01/13 11:36 03/01/13 13:11 03/01/13 11:16 03/01/13 13:15

My scenarios are: Does START B begin prior to START A? If YES, Time difference? This I am able to accomplish. I am getting stuck with: Does START B begin prior to END A? If I have a YES, I need it to give me the difference in minutes, and I am unable to get the correct number of minutes when it's over 60, which is the second row of times in my data.