How many more days should I wait before carefully cracking it open to egg topsy?
I typically start off responding to this type of question with a question, are you counting the days right, so don't be too offended. This is a real common mistake on this forum. It takes 24 hours for an egg to have a days worth of development. So when you start counting you say "zero" when you put the egg in the incubator or under a broody and wait until the next day to say "one". An easy way to check your counting is that the day of the week you set the eggs is the day of the week the 21 days is up. If you set them on a Friday the 21 days are up on a Friday.
I'm not saying that is the day they should hatch, that's the day 21 days are up. I've had eggs hatch a full 48 hours or so early under a broody hen or in my calibrated incubator. Others have had them hatch under a broody hen two full days late or even a bit more. The 21 days is the target but there are different reasons they may be early or late. Heredity, humidity, how an how long they are stored, and just differences in individual eggs can make a difference. A big factor is average incubation temperature. If the average incubation temperature is a bit warm they can hatch early. Cool and they can be late. It's even possible in an incubator for one spot to be a bit warmer or cooler than other spots, especially in homemade incubators. Before a chick hatches it absorbs the remaining yolk. A chick can typically live at least three days off of that yolk without eating or drinking. It's nature's way of letting the early hatchers wait on the late hatchers.
My incubator hatches are typically around 20 chicks. Most broody hens get 12 eggs. Some of my hatches are totally over within 16 hours or so of the the first one to hatch. I like those. I've had some last over 48 hours and into the third day. What a pain. I had a broody hen hatch her first chick late Monday and not bring them off the nest until early Friday, about 3-1/2 days. I had one incubator hatch where one single chick hatched one evening and nothing for a full 24 hours. No pip, no nothing. Then I saw a few pips just before I went to bed. By the next morning when I got up I had 16 more chicks and the hatch was over.
I've gone through all this to try to answer your question, when to give up. When is the hatch over? I don't have a clue. I let my broody hens decide when to bring the chicks off the nest, those broodies know more by instinct about being broody than I'll ever learn. I let the broody hens take all that stress off of me.
With an incubator it can be rough. After all these years I go by feel more than any hard and fast rules. Each hatch is different and has its own feel. I generally wait 24 hours after the last one hatched without seeing a sign but that would have been a disaster with that one hatch above.
Sorry that last one did not hatch but 8 out of 9 that developed is pretty good. I'd be happy with that.
