If you are familiar with visual basic or modifying macros try this
Add this code to a module in the workbook
Function Timediff(startT, EndT)
Dim timediff1
timediff1 = DateDiff("n", startT, EndT)
If startT > EndT Then timediff1 = timediff1 + 1440
Timediff = TimeSerial(Int(timediff1 / 60), timediff1 Mod 60, 0)
End Function
then in the sheet where you want the calc to take place use the function Timediff
ie if start time is in cell D3 and end time is is cell D4 and you want the time difference to display in cell D5, type
=Timediff(D3,D4) into cell D5
You will need to format cell D5 to the time format for it to display correctly.
for info the "n" in the Datediff function is for Minutes and 1440 is obviously the number of minutes in a day.
PM me if you need help in adding a module as I don't know your experience level in
VB and don't want to tell you how to suck eggs.
MAx