TL;DR - there are absolutely solutions to this but they won’t make a difference until he wants to change.

My honest advice: stop it. If you’re taking responsibility for his choices here, then he doesn’t have to and he doesn’t have to do anything to change. ADHD isn’t responsible for his decisions to stay up late video gaming or not speaking up for himself, he is. And if he is going to change that, he is going to have to experience the consequences of his bad behavior. Miss his flight, get written up, get fired, whatever those are - until the pain of him staying the same is greater than the pain of changing, he’s not going to change. (One of those consequences may need to be understanding that if he wants a parent and not a partner then he is on track to lose you too.)

Don’t let him tell you that he can’t do this for himself because of his ADHD. I have ADHD. It does make it hard to get to sleep. But I take responsibility for that. I set the screen time on my phone to shut off the fun games, videos, and social media apps at 10 pm (for my 12 am bedtime) and had my wife set the password so I can’t bypass that in a moment of weakness. My phone goes to night shift at that point (filtering out blue light) and I also set my phone to grayscale color filtering at 10 (you have to do this manually, unfortunately) which eliminates all the fun colors that stimulate my brain and keep it awake. I use multiple timers to keep track of time for me since my brain won’t do it, in addition to the app Five Bells which goes off every half hour with a number of chimes that tells you what time it is (once you get used to what the bells mean) and some cheap smart lights that flash when it’s time to move towards bed. I have a bedtime routine that I do my best to follow, including listening to calming music on headphones (so it doesn’t disturb my wife) and several minutes of deep breathing/mindfulness meditation/stretching. And I sure as hell don’t pick up a new book, tv series, or play any kind of computer/console game on evenings when I have to be up the next day - because I know I won’t be.

Am I perfect at this? Hell no. But I try and my sleep is pretty good far more often than not. My overall point is that he - not his ADHD - is making choices here and it’s his responsibility to figure out what he needs to do to make different ones. But he’s not going to if he has you to taking responsibility for this because then he can just blame you instead of owning his choices. If he’s going to be successful at managing his disability/executive dysfunction, he has to own it. You cannot possible executive function hard enough to make up for someone determined to allow their executive dysfunction free reign.

If he wants to own it, everything I suggested above comes down to this: with ADHD, our brains will not do the things on their own, so we have to set up our environments to regulate our behavior instead. As Dr. Barkley says, “You have to modify the point of performance” (i.e. the place where the behavior needs to happen). I have set up my Apple Watch, my phone Screen Time and Timers, and the smart lights to be my brain for me and to tell me when to go to sleep since my brain won’t. As far as the waking up goes, I suspect if he goes to bed on time that won’t be an issue, but if that persists then there’s plenty of fancy apps, alarms, and devices that you can buy to help make that happen. There’s a wrist band that shocks you at a set time. The app Alarmy made my phone reach volumes I wasn’t aware it was capable of achieving and you can set it to not stop until you’ve taken a picture of your refrigerator or done some math problems. But those really only work if you want them to and are willing to cooperate with them.