Don't you really have EndTime - StartTime?
What you show is what you get when you select time as the result type.
Use ( EndTime - StartTime ) / 3600 and select Number as the result type. (There are 3600 seconds in an hour)
You can also use time data formatting on your current field to show only the hours.
Gotcha... ok. Made that change and now I've got this showing -4.
START TIME 10:00AM
END TIME 2:00PM
How to I remove the Negative - ?
It shouldn't be negative. 2 pm is greater than 10 am so subtracting Start Time from End Time should not produce a negative.
EndTime - StartTime is 14400 seconds
(EndTime - StartTime ) / 3600 is 4 hours
No negative should be produced in either case. As I pointed out in my last post, you have the terms reversed and are subtracting the larger value (End Time) from the smaller (start time).
(But beware of time intervals that start before midnight and end after midnight. If those are possible, you should use TimeStamp values instead of time.)
it may help to point out that time fields store time as an integer equal to the number of seconds since midnight regardless of whether you use a 12 hour or 24 hour format.