I was setting eggs in the bator last night (for the first time) and this question crossed my mind. I've never heard it addressed so I thought I'd ask: Does it matter what time of day you start the eggs? In other words, if I put them in the incubator in the morning will they hatch in the morning? If I set them in the evening will they hatch in the evening? I tend to think it doesn't matter, but I could be wrong...
It doesn’t matter. Don’t get too hung up on the thought that they will hatch in exactly 21 days. It’s not that precise. There are many things that can affect when a chick hatches, heredity, humidity, how and how long you store them before they go in the incubator, even just plain differences in individual eggs. A really big one is average incubating temperature. If the incubator runs warm, they can hatch early. If it is cool, they can hatch late. I’ve had eggs pipping when I went into lockdown and those hatched on Day 19. I’ve had eggs under a broody hatch 2 full days early. Others report they have had eggs under a broody hatch a few days late. Often when they start hatching, my hatch is over in less than 24 hours. But I’ve had a chick out of the egg and walking around a full day before any other egg hatched. It wasn’t average incubating temperature that made that much of a difference but something else. Hatching is not an instantaneous process either. They internal pip, external pip, then zip and come out. There are a lot of things going on during this process. They have to position themselves to hatch, learn to breathe air instead of living in a liquid world, dry up no longer needed blood vessels, absorb the yolk, do something with that gunk they have been living in so they dry nice and fluffy instead of all matted down, and who knows what else. Some do a lot of this before external zip. Some do a lot after external zip. Some start a lot earlier than others in the process. If you get all your chicks to hatch within 24 hours of the 21 day date, everything has come together perfectly, even some things not in your control. If they are all a day early or late, I would not change anything. If they are all a couple of days early or late, you might want to tweak your incubator temperature.
