Last year my daughter set eggs in an incubator & under a broody on the same day & time. On day 19-20 we saw chicks & heard peeping under the broody. The incubator eggs hatched exactly on day 21. It was summer, so the outdoor temp could have been a factor. The incubator was inside an air conditioned house, so not all variables were controlled. Of course, DD's expanding on the idea in this year's project because one test does not make it a valid experiment.There's nothing more cute than watching a mama with her chicks, but she will definitely teach them to be cautious. The one thing I'm not sure about, that I would be curious to know, is exactly how closely does the mama hatch her chicks to 21 days, and how long does her hatch really take? My incubator may hatch from day 19 to day 22. My broody just shows up one morning with her chicks
Like you, I've had incubator eggs hatch on days 19-23. For me, once the 1st hatches, it's like popcorn for 24 hours. ie- If the 1st hatches on day 19, then the rest will usually be out before day 21.