I need to verify some test cases by backdating my system. How to do this?
I would change the time on the clock back, personally.
Depending on how your domain synchronizes time, you'd take different approaches, but generally the easiest way is to just change the clock in Windows back. Synchronization isn't instantaneous, (it works by speeding or slowing clock ticks until your reach the "correct" time) so you shouldn't have to worry about that.
Although, the thing you do have to worry about is that once you get too far out of sync (+/- 5 minutes by default), you won't be able to authenticate against the domain, which might be a problem depending on what you're testing.
And this all presumes you have the permissions to change the system clock. If you don't, easiest thing would be to get them. If you can't, try killing your network connection and changing the clock in the BIOS, and letting the OS sync to that.