I'd never heard that about why a chicken should lay in the morning. Very interesting. Thanks. Of course, mine don't always.
It takes about 25 hours from the time the egg starts it's journey through the hen's internal egg laying factory until it is laid, though I'm sure the hen can delay it a while if she wants to. I often see a hen pacing in front of an occupied nest, looking in, and telling the other one to hurry, even with empty nests available.
I don't know exactly what triggers that egg yolk to start its journey. All I've read is "hormones". That does not tell me much. I could guess that maybe daylight triggers those hormones to release an egg yolk to start the journey. If so, 25 hours later it would be morning when they laid. Or I could guess that the hen does not want to lay on the roost but wants to lay in a nest, so she holds it until it is light enough that she can see the nest. Again, they would lay in the morning. But I do not know that any of these theories are true.
Most of mine usually lay in the morning, but certainly not all. I have some that lay at the same time each day. I have some that seem to lay just a bit later each day. And I have some that seem to follow their own pattern. Some are time consistent when they lay, though they may be consistently different than others, but some are not. As with almost everything else concerning chickens, they are all individuals.