When you put a hot cheesecake into a freezing cold freezer you get steam. Steam creates ice crystals aka freezer burn. Uneven cooling may affect the way it sets up also. If you want to put into freezer for a few hours make sure to wrap it tightly in plastic wrap after it has cooled down to room temperature. This may avoid having to do an overnight chill. Give it a test and see how it goes but I do not practice this method of chilling.