A delayed sleep/wake cycle is only relevant in the context of a society where people are forced on an unnatural sleep schedule. You could get a full 9 hours of high quality sleep every single night and still be considered to have a delayed sleep/wake cycle disorder.

Some people are just night owls. A large percentage of night owls have ADHD. I think they can linked without it meaning that people with ADHD have to learn to get up at 5AM.

Keep staying up late if that's what feels natural for you, but it's probably worth making sure that you're still getting enough sleep and that you don't have other issues (like sleep apnea) keeping you from getting the quality of sleep you need. There's a lot of other health issues associated with sleep disorders and sleep problems will tank people's ability to focus even when they have non-ADHD brains.