|Jerry, the reason I'm asking all these questions, is that you can CUSTOM FORMAT the cell to Display the number as negative, it's not really a negative, it's just Displayed as a negative.|
Something like - H:MM
There is a second way to calculate a negative, but it involves changing the way Excel determines time values. Something I would not advise.
So if we had a bit more information as to what it is your trying to do we might be able to help more.