Exciting, isn't it, but also a worrying time.
How long it takes them to come out once they external pip can really vary. That chick has a lot of work to do before it comes out. It has to learn to breathe in air instead of liquid, absorb the yolk, dry up blood vessels it no longer needs and absorb that blood, do something to the gunk it has been living in so it dries nice and flufffy instead of matted down, and who knows what else. Some do a lot of this before they external pip. These usually pop out within a few hours. Some do a lot of this between pip and zip. These can take a long time to pop out. Some even come out before they have finished everything. Most of these still make it.
Most of mine are out within 12 hours of external pip, but some people on this forum have posted that they have had chicks take 24 hours between external pip and zip. There is no set time for all of them. Usually when I can hear them peeping but they have not external pipped, the hatch starts with 12 hours, but it can go on for a couple of days. It has taken that long, but most of mine are over within 24 hours of the frst external pip. They follow their own schedule.
There are a lot of risks with helping a chick hatch. If it is not ready to come out on its own, you can kill it. A lot of the chicks that people help hatch die, either then or within a few days.
How much humidity is a hard question. You get a whole lot of different answers because diffferent things work for different people. You'd think the conditions inside the incubator would be the same for every one of us, but that is not the case. Each of us have out own unique circumstances. Ir's hard coming up with hard and fast numbers that cover all of us because someone will come on and say that did not work for them and they are telling the truth.
I personally try to have a minimum of 65% humidity for lockdown and prefer it to be a bit higher. When the eggs start hatching, the humidity often jumps up to 85% or more from the additional moisture released by the hatching eggs. That higher humidity does not harm the hatching chicks at all.
I don't know which incubator you have or what your trays look like. With my 1588, I fill the two middle trays and maybe one of the edge trays, depending on what my background humidity is. I'm very confident other people do differently. There are just so many different things that work that there is no one answer for all of us.
Good luck! I advise paience and give them a chance to hatch in their own. You'll probably get a much better hatch that way.
