A hungry feeder is a dangerous feeder. They will eat the only other thing in the enclosure, aka the snake.
So, make sure your feeders are well fed and hydrated before dropping them in with your snake. They're less inclined to eat a snake if their bellies are full.
I wouldn't leave the feeder in for more than 30 minutes. If your snake doesn't eat w/i that 30 minutes, take the feeder out and wait for the next feeding date.

Personally, I just drop all my feeders in with the snakes and close the tubs. Usually all the snakes strike and coil in a matter of seconds, but sometimes I get the occasional slow eater. I leave them alone, but I'm still in the room checking in on them every few minutes. They usually eat w/i that 30 minute time frame. If they don't, I take out the feeder and save it for next time.