Calculate Date with Time Difference

[OceanBlue]

Attached a screen shot that shows what the application is displaying the date and time value
with time remaining

I need to create a formula that would confirm what the application is displaying

Example

Start the Job on 08-30-2011 8:01:00am
Due date 08-302011 11:59am
SLA Remaining 4H

If I plug in the same figures, i need to confirm that is is True 4H

and if it past due like the attached screen shot, my formula should confirm same numbers.

Thanks