There is another way if you want to keep it as a time field.
Make a new formula as such:
iif ({Time_Scheduled} > {Time_Given}, ctime ({Time_Scheduled} - {Time_Given}), ctime ({Time_Given} - {Time_Scheduled}))
This will give you a record in a time format.
Then you would make the negative values come up as red. You can do this by following the steps below.
1) Place your new Formula Field into the report
2) Right click on the Field
3) Select "Format Editor"
4) Click on the "Font" tab at the top
5) Next to color you will see and icon that says "x+2" click on that icon
6) Scroll to the bottom and enter the formula: iif ({Time_Scheduled} < {Time_Given}, crBlack, crRed)
7) Save and it should work