The biggest problem with leaving those who have been pip for many, many hours is you risk them being shrink wrapped inside the egg by the membrane. I know with you humidity correct all should be well, but as many of us do it's just impossible to not open the bator to look them over and remove shells etc. I had one the last batch in my bator that was pip but never zipped. So afrer about 24 hours I helped it. I didnt take it out of the egg, just made some more cracks around the end it were it has pip. Works great. I have also just left them alone and they will most of the time make it out. But I have also had them die in the shell after piping