Whiz did that because he has attachments to Earth. Mostly because it's where Goku and Vegeta live. Plus all of the food. So I think he didn't do it just to screw over Freeza. The Grand Priest has no such attachments so reversing time would be a bit odd. Plus it would mean he would be strong enough to UNDO Zeno's Universal destruction. Which to me would be a bit too OP for someone who isn't the strongest being out there.