software

I have 2 problems in trying to create difference variables representing
elapsed time between parts of a process:

1. If, say, an appt. was scheduled for 12:10, but the arrival time is
earlier, say, 11:45, Excel (the way I'm calculating it anyway:
Arrival-Schedule IF(Schedulegt;Arrival,1) doesn't seem to be able to account
for the negative result -- (if I'm expressing the concept correctly); and

2. If there are overlapping times between parts of the process, so
UnitAdmission=2:30, but DocAssessFinish=3:45, again, I think it's an issue of
not being able to tell Excel how to calculate this. Normally the Admission
would take place AFTER the DocAssessFinish, so the formula would be:
UnitAdmission-DocAssessFinish, etc...

Help!

Thanks,

Meredith