I have had quail pip before and then take another 24 hours to hatch. Never had it with chickens, but when I have hatched chickens before they have been hatched under a broody hen. Currently I have 6 Jersey Giant eggs in the incubator. I think this is probably nothing to worry about. As long as you can still hear it pipping inside the egg and chirping. If it still hasn't hatched in another few hours, you could try carefully peeling some of the shell back without damaging the membrane to help it.
I hope this helps.