Opening the incubator is BAD - - VERY BAD. It will shrink wrap them and they won't be able to get out of the shell.
If you have not opened it and our just watching through a window - - - then relax.
Some of mine have taken 18 hours to go from pip to totally out of the shell.
I had an emergency this last hatch and had to open my incbator, I shrinked wrapped four other chicks that were in the process of zipping at the same time. I did end up assisting those and have had great results with those chicks. They were boouncing around with everyone else within 24 hours AND they were the same size as everyone as within a couple of days.
THIS is how I helped them out of the shell . . . .
First, turn the shower on hot water in the bathroom. Shut the door and get it all steamy. You need the humidity.
Next, run warm water to the sink. Get a wash cloth wet with warm water.
BE QUICK with the next step - - - quickly open the incubator grap you egg and wrap it in the wet warm wash cloth. This stops it from shrink wrapping more. Take the chick to the bathroom and shut the door. It should be warm and steamy in there . . . .
Where the chick has started zipping, finish peeling the hard shell around the egg - - - YOU ARE NOT REMOVING ALL THE SHELL. Just the ring the chick would of peck out before pushing it open. Under the shell is the membrane layer that got shrink wrapped. Well, between the humidity from the shower and the warm wash rag - - - it should be moist again. SLOWLY and carefully, start breaking the membrane loose in that ring - - - start where the chick had left off. Lay the egg down on the wash rag while doing this. .. After you start breaking that membrane the chick should be able to push the egg apart and finish the zipping.
Rinse out the wash rag in warm water, wrap the chick in it and return it to the incubator for another 24 hours. It will dry off during this time . . . If you have a separate brooder area set up - - you can use it too.
The less times you open the incubator the better, so get some help doing this so that you can remove two eggs at a time if you need too. I would not interfere with the hatching process until the chick has tried for a full 24 hours to come out. Some are out within a couple of hours of starting the zipping and some take a long 15, 16, 17 hours to finish what they start.
I, also, would not interfere with hatching EVEN IF IT IS LONGER than 24 hours unless you opened the cooler and shrink wrapped the chick. It is a LOT better that the chick die in the shell than it dies 7 days later or worse 8 weeks later. Weak at birth is weak later. They will be the first to get sick.
Good luck