My biorhythm is totally out of the window, yet it's what feels best for me. I feel more energetic and active between the early evening and when morning comes and get a bit more tired and a lot more cloudy thoughts during the day. I blame sensory overload during the day... I seem to have a bit of a disposition towards daylight... or bright lights for that matter. I wish I made it all up, but people being busy, loud noises, bright lights on end doesn't really do me many favors.
It's not to say I don't go out during the day; I actually have to, but I often try to do so when my energylevels are somewhat fine, meaning I often go out for groceries when stores just open at 8 am or when stores are about to close past 8 pm.
So, in a sense, being a nightowl... or even being nocturnal (as it seems to fit me more; whereas a nightowl means you probably stay up a bit late... my wake cycle seems to have done a full 180) is how I function and get stuff done.
My curtains usually close at sunrise and open in the evening, so at home I don't really have to deal with it being noon or anything when I'm awake.
And then there's sleep and the need for it... I don't do regular 24 hour cycles and usually sleep a few hours every other day... I try to fit that in during daytime as much as I can, but sometimes I'm exhausted and sleep at night, while I have to push myself with minimal energy levels throughout daytime again. It's not that I don't wake up well-rested, but an active daytime life just drains me so much more than being out and about at night doing things. It seems counterintuitive to force myself in a routine that doesn't work for me at all.
It's interesting though, since in general I don't have a problem sleeping... when I sleep, I sleep great, which is why I never felt the need to "fix" it. Aside from difficulties with potential jobs I can't really complain about my days so to speak. I'm not really suffering from any health issues by not being that much of a daytime person; just have to make sure I get some vitamin D in, since it's usually taken in through exposure of sunlight. For a while I thought if having inverse wake and sleep cycles was the issue, but my energylevels at night are crazy high and suitable enough for me to work out at 4 am or something.
The general thing for me however is, there are so many factors that come in here, both from being on the autism spectrum and personal preference which makes it a bit silly to "fix" nor did any therapist feel there was much wrong with it. Most societal rules seemingly don't apply to me anyway, since job prospects are out of the window, My circle of friends are night owls (just not as extreme as me), hence my social life is fine. I have no issues to sleep or lack serious executive functioning (except for those few things inaccessible at night) and my lack of sunlight probably helps me appreciate winter a lot more without suffering from some kind of seasonal affective disorder or something.