Yes ADHD can impact sleep including making it more difficult to fall asleep and altering the person's natural sleep cycle. People with ADHD are more likely to be suited for a nocturnal lifestyle, I personally prefer when I can sleep from 2pm-2am (CFS needs a full 12 hours) so I'm awake for late night and early morning hours but mine makes my sleep schedule roll so I can't ever have a set sleep schedule unless medicated properly, and that's hard to do too. The best you can do is figure out a bed time routine that is most likely to put you to sleep, I personally exercise/do chores 3 hours out, get ready for bed throughout the next hour, and for the last hour I do something low energy while laying in bed. Most people suggest the last step be screen free as the light and any stressful content you might come across can impact your ability to fall asleep, I personally cannot handle the lack of stimulation and need background noise and usually play stimmy videos or easy puzzle games and avoid social media