I also checked all the eggs I brought up and 2 out of the 6 did not have any movement or any change in them at all. The other 4 had hair pockets and what seemed to be movement from them! mom has 3 chicks with her right now.
I strongly suspect that she will refuse to recognize any chick as hers if it is over 72 hours behind the development of her first peeps. That doesn't mean that she will kill that chick because a younger chick does not represent a danger to her own chicks, but only that she will not do the normal mothering behaviors.