You couldn't bring yourself to sleep before midnight even when waking up at 5am on regular basis?
I consider myself night owl too, nowadays I fall asleep at around 1am. But I used to work in construction, getting up at 5:30am every day and just after couple weeks of this routine, I would fall asleep at 10:00pm - 10:30pm, usually while watching TV :)
I'm a night owl, and a few decades agoI was on a rigid Army training schedule for months at a time, where we would be released for the night around 1am-2am and already have roll call at 6:30am; I would still not fall asleep until 3-4 am. (This was not physical training, although we did do a short physical exercise daily, and a an hour long one three times a week)
My pre-army reserves carried me through the first 3 months, and then I would just uncontrollably crash for 20-30 minutes at lunch time. My eyesight deteriorated significantly (much improved after I started getting some sleep again, thankfully, but not as good as it used to be, unfortunately) and I'm sure my body was otherwise harmed, although I did have more waking hours than at any other time I can remember.
This is why you were able to fall asleep! If I get up early (~6am) in the morning, my body just doesn't seem to care -- I won't fall asleep (or even feel truly tired) until about 2am.
Unless I actually do something physically taxing during the day.
I consider myself night owl too, nowadays I fall asleep at around 1am. But I used to work in construction, getting up at 5:30am every day and just after couple weeks of this routine, I would fall asleep at 10:00pm - 10:30pm, usually while watching TV :)