There are two kinds of time, clock time and elapsed time. Clock time is a twenty four hour clock. In clock time math 23:30 + 60 = 30. Why? Because 23:30 isn't twenty-three hours and thirty minutes. It's 11:30 PM. And adding 60 minutes (one hour) to 23:30 doesn't get you to 24:30 (which doesn't exist on a clock) it gets you to half past midnight the next morning.
Elapsed time is different. It's a number of minutes (or seconds or other unit) and can be added together getting numbers bigger than 24 hours as necessary. The proper unit for elapsed time is (counter intuitively) not TIME but rather INTEGER. If you have two TIME values and want to figure the interval between them (assuming they're in the same day) you can subtract the smaller (earlier) from the larger (later). The result will be an INTEGER number of seconds. You can then use this INTEGER value in addition operations with other similarly derived INTEGER values to get the total elapsed time. -- Larry
