For chickens, I usually give them 24 hours before I consider helping. If they die between pip and 24 hours, the chances of them being able to make it if you help are pretty slim- they may also be resting and absorbing yolk still, especially if they are early pips. If it's been 24+ hours, and they're alive, they've probably been pushing but need a little help. I will then create a thin zip line in the shell for them and leave them to sort themselves out for another 12-24 hours. That generally gives them time to rest and then push out through the zip line I made.