X2 - leave them in there until the last one hatches, up to 3 days as mentioned. I did leave a chick in for 3 days once and he had was very vigorous when I took him out. I have only ever had one chick die in the incubator after hatching, and that one was malformed and would have likely died even faster in a brooder. I have lost many chicks from drying out while hatching, until I learned to leave the hatcher closed and really increase the humidity while hatching, to at least 80% if possible (it has hit 99% at times with a bunch of wet chicks in there, and no problems at all). My hatch rate got much better overall once I learned to leave the chicks in the incubator longer.
I also learned to not rush giving them water in the brooder after having a small chick drown. As long as some are unsteady on their feet, all they get are crumbles scattered in the brooder floor, once they are all running around, then adding a waterer is safe, since they can step out as easily as they step in.
Experience is a great teacher, though I feel bad about the chicks that gave their lives to teach me. Hopefully, their deaths help more than just me.