I just had to help on of my chicks out of the shell. It had pipped the shell on the wrong end. I have never helped any chick that has not managed to pip a hole in the shell. If after a full 18 hours or more without any progress, I will peel the shell off the membrane very carefully, starting at the site of the pip. I try to peel shell around the egg in a 360 degree fashion. Usually they are very dry and you can put them egg back on a damp cloth or paper towel. It is best to watch them at this point and see if they are still trying to break free. Trying to peel the membrane can cause bleeding as the veins that formed early at attached. You must proceed very carefully and slowly to allow some freedom for them to move. Once a chick is stuck it is extreamly hard for them to hatch. I did have anothe one in this batch that hatched all by its self from the breech position, ( the small end of the egg) They can some times make it out, I watch carefully to see if progress is being made before I would interfer, It there is a vital little guy in there desperately trying to hatch, I can't just leave it especially when I know that there were less than desirable conditions, temp spikes or humidity issues involved that may have contributed to the problem it is having.
It is a tough call and when in doubt it is best to let mother nauture make the decision but with that being said, the ones that I have helped are all growing and are active healty chicks.