Older kids

Those of you with older kids (specially ones with adhd) do you have trouble with your kids acting up worst when they have screen time/tv time. Idk why but my 8 year old son gets a really bad attitude when he’s allowed longer screen time/tv time...I really don’t understand it at all. Today we were trying to have a movie day because we had a snow day and he had such a bad attitude when it was time to take a break (I would make him read for a little while in between movies) then he ruined the last movie because he had such a bad attitude and was being disrespectful toward me. I don’t understand it at all. Last week he was grounded for a full week from tv/screen time and we didn’t have nearly the attitude problem that we would have if he had his screen time. And I only allow 2 hours of screen time a day during the week and a little more on the weekends, on a occasion rainy day I will let him do it practically all day (because who doesn’t like a lazy day every once in a while) but then I regret it because he has such a bad attitude it’s not even funny. I really don’t understand why this happens (I wasn’t like that as a kid and neither was my husband) ...does anyone else have this issue? He also constantly asks for the iPad, PlayStation, DS etc...until I made it a rule that if he’s asks then he will loose one minutes of screen time every time he asks for a electronic he learned really quick not to ask.