45 minutes to an hour has always worked out just fine for me. Any less time than that and there is difficulty getting it off. Usually if you do the whole car, go get a drink or a smoke or whatever, and then come back to the car and start buffing it off in the same direction you applied it then you are fine. Its probably been 45 minutes since you applied it to that particular panel and by the time you get all the way around you should be fine. You could dress the tires or do something on the interior while you wait too. Its important not to cheat the time on it. Give it at least 45 minutes.