I am on day 22, with a couple eggs not yet externally pipped, while the rest of the eggs already hatched on day 20 and 21. I have 2 marans eggs that I candled last night and could see that they internally pipped (18 hrs ago), and I can hear chirping if I tap on the shell. But no external pips from either. They may be small chicks, maybe not strong enough to pip through the thicker shells, because each lost about 17% of its weight while the others lost less. Anyways, I wondered how much longer to leave them before they run out of air in there?