They have 10 minutes max before I re-check if even, in my experience if they don't eat soon as I drop the rat, they probably won't (at least for adults) and if it is the case the rat just go in it's corner and groom itself.
Hatchling well it depends but than again when you feed and hatchling the prey can stay longer without posing a risk, fuzzy rats have never hurt anything.
The key to really get a strong feeding response is consistency (feeding the same day every week) and pre-scenting the room by leaving the feeders near the enclosure an hour prior to feed, if you do that the rat will rarely have the time to touch the floor of the enclosure.