I just read the abstract. Does he address the objection that nocturnal animals sleep in the day, and length of sleep doesn't change as much as the length of day over the seasons?

If your eyes are closed, does it matter if it’s daytime?

Oh maybe I misinterpreted. I thought the author was arguing that the purpose of sleep was this protection of the visual cortex, but maybe the idea is that sleep has another purpose (with varying timing thoughout the day depending on the animal) and the purpose of dreams is to protect the visual cortex while this is going on.

I've read a bit about the scientology cult and their hypnosis technique seems similar. This article mentions that the sleeping person hears the command or question as a megaphone type of sound definitely coming from outside the dream. Perhaps an average person perceives such a "megaphone narrator" as trustworthy and remembers the heard commands as important.