Warning than after. But not by a lot.
Before: you force another play and it's 3rd down after the 2 min warning with 2:00 left.
After: it's 2nd down after the 2 min warning and you call your TO right after the 2nd down play is over so it's 3rd down with 1:53 left.
It's all moot if you let them get 1st downs or TDs tho 🙂