If you are having cold weather or they got really cold in an AC room, it might affect them. If they are that close to hatch and no date mixups, then I can't imagine that a brief temp flux inside an insulated box would compromise them. What did the temp drop to? For how long? And more importantly at this stage, did they dry out or did the humidity remain in an acceptable range? You know Mom gets off them daily, regardless of the weather. My broody hens don't know that it is LOCKDOWN!!! Hope all goes well. I read others on here saying to give the late hatches until day 24 at least, especially if they are still moving inside. If your temp was on the low side of the range already for most of the 21 day period, I read that the hatch can be delayed anyway. Good luck and keep up posted.