Ok try to remember this. Chickens take 21 days. That's what all the books say, but maybe they're just making this up and really want you to be surprised when chicks hatch on day 20, right?
So here's the unvarnished truth. Chicks can hatch when they feel like it. Girls first Boys second cuz it takes longer for boys.
Seriiously they can and do hatch when they feel like it. They may start pipping on day 20 but not finish hatching til day 23. You just have to be patient.
Like the song says. " you can't hurry hatch, you just have to wait, you got to trust given time, no matter how long it takes". "how many dud eggs can I staannd, before I hear a peep to let me live again". "Seems the only thing that keeps me hangin on..................