I had a nWoD Mage game a while back with a time mage who had selected Postcognition as a rote. In the book, the spell is a covert, and so provides no paradox. The mages quickly discovered that as long as they had their focus, and sealed the room from sleepers, they could continue to use Postcognition indefinitely until the determined the time of the event. Regardless of how small the die pool is, or how brief a window they gained, they could continue repeatedly until they achieved the information they needed.
I could not find a good rule within the system that would prevent this from working, and caused all crime scene investigations very troublesome as the players could look back and watch enough fragments from the scene to piece it together.
Was I missing something? I don't like telling players "you can't do that because I don't want you to". I feel that a better answer is needed.