It can vary a bit. Remember that 21 days means 21 full days of development. If incubation started on a Sunday, they should hatch on a Sunday. Some can be a day early, some can be a day late, but most should hatch around 21 full days of development. And hatching is not an instantaneous thing. They pip. They rest, maybe 12 hours. They zip. They push out. They dry off. You can possibly hear peeping but will probably not see a thing until some heads start peeking out.
The best thing you can do for a successful hatch is to not disturb them, hard as that is. Mama can get upset and hurt her chicks trying to defend them. She has to do some serious temperature and humidity control right now. If she is disturbed, she might take her chicks off he nest early. I did that once on the farm growing up and Mama left several eggs unhatched, all due to my interfering. Hard as it is, especially with children, let her do her job.
I have a first time broody hen egg hatch so far there are five and a couple more are pipped, but when I peeked the hen pecked at the chicks, almost like they were intruders, then when they got underneath her and quieted down she stopped, should I be concerned?
I suspect Mama was pecking at the chicks to tell them that there is danger out here, there is a big threatening intruder, so you get back under me where it is safe. I personally would not be concerned about her behavior.