Yeah, the average lifespan of a live rat in a ball python enclosure is about 6 seconds. Sometimes, the rat barely gets to walk a few steps, lol. Seriously, if the snake doesn't eat the live rodent within 2 minutes, it is not going to happen. I would never wait 15-20 minutes, snakes are not going to wait that long to take an opportunity for a live meal. They are going to kill and eat immediately, or ignore it.