Make sure that the time you enter is recognized by Excel as a time.
Enter an after-noon time, say 13:00
Using cell formatting:
a. set the format, selecting from Time, a format with PM
look to see if the cell shows 1:00 PM or similar
b. set the format to a time format without PM
look to see if the cell shows 13:00 or similar
If this works, then the times have been recognized by Excel as times.
Excel holds times in the decimal part of a number
(1 is the equivalent of a full 24 hour day).
0.5 is 12 noon i.e., half-way through the day.
To get the difference just subtract the earlier cell from the later cell.
Enter 07:30 in cell A1
enter 16:00 in cell A2
In cell A3 enter this formula =A2-A1
The value in A3 is displayed as 08:30 if the cell is formatted as hh:mm
If you format A3 as a number with 4 decimal places it will show 0.3542 i.e. just over a third of a day.
To get hours and minutes out of A3,
in cell A4 put this formula =HOUR(A3)
in cell A5 put this formula =MINUTE(A3)
and you will get 8 and 30
In A6 enter =A5/60
and you will convert the minutes to fractions of an hour, i.e., 0.5 in this example
Hope this helps with your calculations.
PS Excel stores dates in the same numbers as times, its just that the date is in the integer or whole number part of the number.
04-Nov-2009 is 400121.00, 05 Nov will be 400122.00
12 noon on 04 Nov is 400121.50
Excel starts counting days from 01 January 1900