Many chicks pip 24 hours before they zip and hatch. It's hard to watch them and not do something. I keep a close eye and if their movement, peeping, breathing starts to take a nosedive, I pull the egg and open the pip hole a bit more. I agree with trying not to open the bator too much. I have a side door on mine and lose hardly any humidity/temp.
BTW...I had one lone egg...a White Langshan...that I put in later than those in my last hatch but couldn't remember when. I left it in there and added new eggs, not really worrying too much about the humidity. I tend to "dry hatch" with good results. At any rate...I woke up this morning to a just hatched chick. And the humidity hasn't been over 45% anyday this past week. Just sayin'....