I have an egg in the incubator that's been cheeping for about the past 4/5 hours. The egg has a small crack, almost like a pip going inwards that has been there for a few days, presumably caused by the hen at some point. Apart from this there is no sign of an external pip. I candled the egg and the chick is fully in the air cell now (I know I shouldn't be candling etc at this late stage - it's a long story but the hen left the eggs day 21 so I've had to candle to see what is dead/alive and what stage it's at). All the other chicks have had to be assisted, the ones I haven't helped have died. So my question is at what point do you intervene and make an external pip yourself?