I just wanted to post a follow-up since so many times I have been left wondering how a situation turned out because the OP never came back to give an update.
I want to thank you again for your advice - I did "sit on my hands" and wait - and that little chick did eventually zip and hatch. I also appreciated the info about how you helped the two that got glued in their shell, because I had that happen to two of mine too! They both zipped half way, one at the wrong end, the other in the middle, and then stopped. After several hours and when it was apparent they weren't going to make it out on their own, I gave them a little help and they both seem fine now, a week later.
Anyway, to anyone reading this, worrying about a chick that pipped but hasn't started to zip after 24 hours or more, consider just "sitting on those hands" and giving that chick a little more time. My little Silkie took THIRTY FOUR HOURS from pip to zip - and then hatched in about 15 minutes