I agree they should be perfectly fine without heat at this point, day or night.
Have you gotten a temperature reading inside the coop? I'd worry more about heat exhaustion than being cold, since you mention wanting to confine them to the coop, but I don't know what style of coop you have.
Have you gotten a temperature reading inside the coop? I'd worry more about heat exhaustion than being cold, since you mention wanting to confine them to the coop, but I don't know what style of coop you have.