Calculating elapsed time

I am developing a worksheet in which I need to calculate the elapsed time from the date and time that a doctor dictates a report to the date and time the transcriptionist finishes transcribing the report. The formula has to include both the date and time of each of those transactions in order to get the exact "turnaround time" of that dictation.

Simply a case of subtracting the start date and time from the end date and time then formatting the cell to show the result in the way you need.

So if start time was in A1, end time was in B1 and you want the result in C1, use =B1-A1 and format to something like [HH]:MM:SS