Sick chickens will lay eggs during the night or very early morning hours. I researched this last year when I had a hen lay a weird egg. It turns out that when chickens have an egg get stuck, due to reproductive troubles, they will often drop the egg during the night or next morning, after trying unsuccessfully to lay it during the day. They don't actually lay the egg at night. The stuck egg actually just drops out on its own. When you find an egg in your coop very early in the morning, that is usually what happened. This could come from chickens who were fed the wrong type of food from 8-20 weeks old, which forced their reproductive organs to grow too fast.
That said, I do have a Sebright Bantam who on two occasions, last night and March 20 of this year, stayed in her laying nest, under the laying boxes, all night.
On both occasions she had not laid an egg during the day. On both occasions, when I checked the next morning, there was an egg in her nest that she had laid. Last night I had checked about 9 p.m., and she hadn't laid the egg yet, though she was clearly trying to do so. So she laid it sometime between 9 p.m. and 6:30 a.m. this morning.
On March 20, when she also chose to sleep in her nest rather than on the perch, I got worried and checked on her at midnight. She hadn't laid an egg when she had gone to bed about 7:45 p.m., but there was an egg in there at midnight, so she had laid it sometime between 7:45 p.m. and midnight.
I hope she's not sick. On both occasions she has seemed fine the following morning after sleeping in her nest all night. I sometimes wonder if she might be trying to go broody? One week ago she seemed to be contemplating laying an egg, and I was in the run, cleaning, and she tried to attack my foot, as if she didn't like me being in her territory. She did the same thing to my male friend that day.
She didn't do that again until yesterday, in the afternoon, when she was starting to try to lay her egg. I have read that such aggressiveness in hens is usually a sign of going broody.