For different reasons most eggs are laid in the morning but they can be laid any time of the day. It takes an egg “about” 25 hours (there is a lot of leeway in that about) to go through a hen’s internal egg making factory. Most hens release the yolk for the next egg “about” (there is that word again) 20 minutes after the egg is laid. So it’s normal that a hen will lay a little later each day. Part of the trigger that causes a hen to release that yolk to start the next egg is daylight. If it is too late in the day the hen won’t release a yolk and will skip laying the next day. I’ve seen hens on the nest laying when the others were going to bed. Normally a hen will not lay after dark though, the daylight trigger to start the yolk prevents that.
I’ve had hens that lay exactly the same time each day, in the morning. Whatever the triggers to release that yolk are and how long it takes for her to get her egg through that internal factory it works out to 24 hours. Some hens don’t lay every day, maybe once every two or three days. These normally lay in the morning because of the daylight trigger to release the yolk.
A lot of people confuse a pullet just starting to lay to a hen that is an established layer. There are a lot of parts to a hen’s internal egg making factory. Most get it right to start with but some pullets just don’t have full control of that process when they start. An established laying hen should have full control. It is not unusual for a pullet just starting to lay to drop an egg wherever she happens to be, on the roost at night or just walking around. Again most pullets get it right to start with but it is not unusual for a pullets first eggs to be soft-shelled, no-shelled, extremely hard-shelled, yolk only, whites only, double yolked, or otherwise pretty darn weird. It just takes them a while to get all the kinks out of that internal egg making factory. There is nothing to be worried about in all this, it should clear up in a few days, a couple of weeks at the most.
As Chiques Chicks said there are always exceptions but the majority of the eggs laid under the roosts are there because a pullet just starting to lay accidentally dropped an egg overnight. I did have a pullet that continuously laid her eggs from the roosts at night. It took me two months to figure out which one was doing that. Really frustrating. I permanently removed her from the flock because there was something wrong with her instincts.
