Is being nocturnal a disorder?

Morningness/nightnes: There are predispositions people have been more lark vs. Owl. When it turns out that person is going to bed in the morning (sleep phase is delayed to this point) and then person sleeps during the day, this can be disorder. It may work to person's advantage with a particular job. If the person does not want this to be the case then it would be a disorder and treated.