The problem why you get the negative value is logical. You wire a value to the Seconds To Date/Time function. This results in two different date/time clusters.
Let's say cluster one contains as a time 14:12:55 and the second contains 12:25:33.
You subtract the second from the first one so you have 14 - 12 = 2, 12 - 25 = -13 and 55 - 33 = 22. It rather would be 27 seconds to fill the minute of cluster two, 34 minutes to fill the hour, 1 hour to math cluster one plus 12 minutes and 55 seconds. This results in 1hour, 46minutes and 82 seconds. These values should be recalculated to 1hour, 47minutes and 22seconds. As you can see, it is not that simple to calculate the time. You can not just subtract the two values.
If I have to calculate times, I usually have a vi like the one attached.
I hope this helps you.
Using LV8.0
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