I practically always leave some chicks in the incubator for more than 24 hours. The hatch is not instantaneous. It will be spread out over a period of time, sometimes maybe 18 hours and sometimes over two days for me. Chicks can go without food and water for three days or more thanks to then absorbing the yolk. With a normal hatch, an extra 24 hours in the incubator at incubation temperatures and humidity will be fine.