I hatched 7 of 14 on Monday. All of the different information that I have read is that not much is going to happen after the initial hatch date, but there is always potential for at least 2 days afterwords. I am new to this but I have lots of time to research. there are so many schools of thought on this you can never be sure what will happen.
My experiance has been that if your temps are off enough to delay the hatch, the whole hatch will be delayed, not just some of the eggs. If I have a few hatch on the due date that's probably going to be all that hatches. Most of the time it seems like the late hatchers if there are any have issues that kept them from hatching. I very rarely keep eggs in the hatcher past day 23 if some of them have already hatched.