I don't open the incubator during hatch unless there is a serious problem. Chicks absorb the yolk so they can go three days or so without food or water. That's why they survive being shipped in the mail.
This does not happen all the time, but if you open the incubator during the hatch it is possible to shrink wrap a chick. That's where the membrane inside the egg dries out enough to shrink around the chick, trapping it so it cannot zip and hatch. I've done that before so I'm convinced it can happen. But the risk is only when an egg has pipped so the membranbe can dry out. And when I opened the incubator, I did not shrink wrap every chick that had pipped, just the one. So it is something that can happen, but does not always happen.
I don't worry about them playing rugby with the unhatched eggs. I've never seen that to be a problem. Some people get real concerned about it and put their eggs in a carton, pointy side down and with the bottom cut out of the pocket to give good air circulation. Some people don't.
How long to give the unhatched eggs is a good question. I don't have a great answer. I've had hatches stretch over two days, but have never had one go so long that I had to take the early hatchers out. Them absorbing the yolk so they can go three days really helps.
