Knowing when to help is hard. Before a chick hatches, it has to absorb the yolk, dry up blood vessels outside its body, and who knows what else before it can enter the world. Some chicks do a lot of this between internal pip and external pip. We like these. Some do most of this prep work after internal pip. These are the ones that drive us batty. Some don't totally finish before zip. A lot of these still actually make it. The chick is not just resting between pip and zip. It often has a lot of work to do to get ready for zip.
It is not at all unusual for a chick to take 12 hours or more between pip and zip. Not at all unusual.
If you interfere too early, you can kill the chick. If you wait too long the chick can die. Some of them are just not meant to live anyway, whether you help of not.
I usually don't help, on the theory that I want strong healthy chicks in my flock for breeders. If a chick has problems hatching, then its offspring could inherit this problem. But a couple of times I have helped. If you see a yellow foamy liquid coming out of the pip hole, it is now or never as far as the timing goes.
