I need to fin how many minutes are between two hours...for example:

10:30am to 1:30pm

I have tried to subtract both times and then custom format the cell [mm]
which will work......but I am trying to make another calculation with that
result and it gives me a number that really is not what I expect......it
should be a simple subtraction 180 minus whatever number.

is there an easier way to get the total minutes between to times without
having to custom format the cell?.....thanks