You can always hear them chirping in the egg, in fact I have only hatched twice in an incubator and they always chirp within 24 hours before hatching. The mother hen would also cluck to encourage them out, so infact, leaving the hatched chicks in there is a good idea as they'll encourage the slower ones out. It's best to leave them in there at least until they are dry, but I also never move a solo chick into the brooder, they like to huddle together.
That leads me onto another point about the brooder, hang your heat lamp above one end of the box, if your chicks are constantly huddled under it they are a little cold so lower the lamp, if theyre scattered around the box they may be too hot. I also offer my newly hatched some very mashed cooked egg, they love it! then when theyre a couple of days old they go onto chick crumbs.
Keep that humidity up, and if you do need to snatch a couple of chicks out (which is very tempting!) have a warm bottle of water so you can quickly spray the other eggs to stop them being shrink wrapped. But try and avoid opening where possible. Its best to raise the humidity a couple of days before hatching and leave it all closed (a phrase commonly called 'lock down').
Good luck, post some pics when theyre hatched!
