No not how old the girls have to be, all seven of my hens are laying. Just wondering how long after they go into the nesting box how long it will be before they lay their egg. I have checked on the girls with one or two of them in the box, I go back out a half an hour later and they are still in there. My boxes are attached to the side of the coop below the roosting poles so I do not believe they are roosting there, just in there to lay their egg. Sometimes it seems it takes up to an hour before they are done. Not that this is a problem per say, but with colder weather coming and I have no intention on heating the coupe until it hits a minus 10*f on a regular basis. I am concerned about frozen eggs. I have already had a few this year.