I've always given my chicks a night. I use reptile heat bulbs so they have the warmth while still getting enough sleep.I read an article that recommended using lighting in an incubator either for 12 or 24 hours a day would improve hatchability and result in less stressed chicks and also using red LED lighting can be used for same reason. It was also recommended that light was left on for a few days during and post hatch to enable the chicks to eat and drink 24/7 in the most important days following hatch.