On a fundamental level, there's no way to draw a line demarcating owls, and otherwise non-owls. It's a false dichotomy, founded on behavior alone, which is subject to peer influence, and other sources of behavior modification. All people lead lives distorted by circumstance, particularly when it comes to circadian rhythm. The behavioral effects of daylight savings time prove this. Casual caffeine consumption is another fact to poison the well.
Anyway, I'm routinely up until three or four in the morning. I despise getting up for a nine to five work day, but I do it. Every chance I get, to sleep in, I take it.
Many times, what's really going on, I've discovered, during periods of extended vacation or unemployment, is that I wind up in rotations that push my bed time forward by a couple of hours every day, and then I sleep for any number of hours, until my body need me to get up, and begin my routine. This pushes me all the way from a midnight bed time, around the entire clock, realigning with a midnight bed time in less than two weeks.
Technically, this is classified as a disorder:
https://en.wikipedia.org/wiki/Non-24-hour_sleep-wake_disorde...
When I get locked into as static 9 AM, alarm induced wake pattern, this frequently expresses itself as pulling an all-nighter, just to realign with the totalitarian nature of the work week, such that I might arrive to work on time, for some bullshit, daily 10 AM scrum stand-up, or whatever. It also leaves me really fucking moody, including symptoms of seasonal affective disorder.
But you know what? I'm not crazy. I'm not sick. I'm just forced to live my life on other people's terms for economic reasons, because I wasn't born into a trust fund, and I'm not otherwise independently wealthy. So, by corollary, I cannot tolerate the idea of being taxed financially, to treat something medically, when it should not actually require medication.
Anyway, you have to account for the proper modular math, when declaring that night owls "simply do not sleep in" nor can you claim that your supposed version of a night owl never experienced fatigue, after 10 hours of undescribed daily activity, due to the psychological cost of an ego facade, or whatever.