They can take a break from hatching for almost 24 hours.Is there any movement at all? If you choose to intervene, be careful, only break the shell, not the membrane more than a little spot, if it is not already broken, for air, and keep it moist in the incubator. If you see small red blood veins in the membrane, stop. They are not ready yet. If there are no veins, then you may continue cracking the top of the shell the way you saw the others do it for themselves. Be very cautious.
Never pull an chick out, after you remove the top portion of the egg, lay it on it's side so the chick can push itself out. It is still absorbing the yolk sack.