This is going to be difficult, for two reasons.
First, the difference is not 2 hours, it's 3 hours
Second, Excel struggles with negative time.
If you just want to display a negative result, and are not going to use that result for any other calculation, you could do something like this
and format the result as number, with 2 decimal places, to show -3.00.
BUT, if you start having fractions of hours, such as 3h 30m, this would show as -3.50, not -3.30.
There are ways round this, but it gets complicated.
Perhaps the best solution is to use something like
You could then have another formula which displays a message if the max and min are not the normally expected way round.