I don't worry about it too much with mine and view it more as is he doing it to the detriment of other parts of his life rather than arbitary target times.
He's autistic and has little spare social battery, so communicating with a couple of friends online is opening up more than he would do in the real world. Talking to his school friend's mum, friend is the same, plus they live at the other end of town so logistically hard to drop in on each other anyway.
Between dyslexia and autism, he's not a book lover. He satiates his thirst for information from youtube which is more accessible than getting that information through wriggling, blurred text in niche books.
He does Warhammer as a creative and social outlet. There is a cap on what he can invest into that due to costs. He's a Lego fan too.
He does DoE award, running (both parkruns and independently) and a martial art. He's fit and active. He also has a significant walk to the bus stop with a heavy school bag. DoE means that he volunteers, and he is self-motivated at setting goals and strategising them.
He's doing well with school, self-motivates on homework, and his youtube documentary interest is a positive to his learning. He also does his share of household chores.
His screentime is watching decent quality/ special interest youtube, or playing strategy/ construction type games that require thought.
Last summer I was mulling all this over and came to the conclusion that his teen lifestyle isn't vastly different to mine. Admittedly my 386 didn't have internet access, but I did spend a notable amount of time on my PC (or my brother's SNES when I could get away from it). I did read/ draw more, and there was more teen-friendly TV on weekend mornings. I did less sport/ physical activity.
I am watching the space more closely with his younger brother, mainly that he likes more PVP type games and they can hype his mood. He is also easier to draw into doing things with me, so easier to divert into something else.
Both of mine find school intense and draining and they need a decent amount of autonomy in how they unwind. As long as they're fit, healthy, cover other aspects of their lives, and aren't exposed to toxic content, they need chance to unwind without external pressure. Micro-managing does not result in healthy outcomes down the line either.