Pip is hole in the egg, through the membrane, for oxygen. Zip is when they start to extent that pip into a line, through the shell and membrane, around the crown of the egg.
It's fun watching them hatch, isn't it?! I love it.
A coturnix can take 24 hours from pip to zip.
Personally, if I know my humidity is good my rule is not to touch anything. The time I helped a chick hatch it died and I believe that some don't hatch because they can't handle it. I'm not one to set up an intensive care unit for the birds so...