If he is not out within 24 hours you can help him a little.but do not help him out all the way, because if they can not get through the eggshell all the way then they are to weak to live.
You will be fine, if your ducklings are pipped make sure you raised your humidity a little so that the membrain does not dry out to much, after they pip they usually rest for awhile. In a few you will notice them zipping. If its more then 24 hours its ok to help, take is slow, if there is any sign of bleeding, stop and put the egg back in the incubator and leave it alone, check it in a couple hours If no progress you can try to help it a little more.
I have helped MANY MANY MANY ducks chickens etc from the shell and have YET to loose ONE because I helped it and it.