By default, kids of that age will want to play but don't have strong feelings about what. If you let them, they will spend all day with one thing and not get bored with it. Now each kid is different, and that may not hold true in the extremes for your son, but generally, I find that it holds.
Let's talk about different kinds of electronics and screen time. It's important to be able to pick out the differences.
First, there is "TV Time", that is just what it sounds like, and this can be a great thing if done in moderation. Children at that age learn by mimicking, and TV and youtube can be great tools to teach some skills. But you always want this to be in moderation.
Next is "Addictive Game Loop" time. Think of this like video game time. It can be on the switch, phones, or tablets. Anything that has that reward of doing a task unlocks the next "level." This needs to be strictly limited. Examples of games like this could include Clash of Clans, Farmville, and Simpsons, especially if there are microtransactions. These games are not evil, but at that age (and even for many adults), that game loop can be a really negative thing. This should be avoided.
Then you have "social games." These are games that are played with other people. Specifically, games that may be played with kids their own age or other family members. Care needs to be taken here to ensure you know who your child is playing with, but generally, these are good games to play.
Finally, there is a category of games that I would call "skill games." These games teach a specific skill, like math or spelling. They can also teach more complex thinking, like planning or logical thought. These are also good games to play.
With all that out of the way, I suggest that you focus on making sure there are good choices available for screen time, then making sure that screen time is broken up. For example, Here is my son's general schedule.
8-3 - Home School, no electronics. If he finishes his work early, he can read on his nook. (We needed to do this so he didn't race through his work to play on his switch)
3-5 - 1 Hour of video game time.
5-6 Swim Team or other structured exercises
6-7 Dinner, and we listen to the news together and talk about it.
7-8 Structured Game Time - We play games together that work on problem-solving.
8-9 No Electronics, other than the nook
9 Bedtime.
On the weekend things get a little different.
Saturday
8-5 - very few video games unless we're playing together. We tend to focus on chores and other things.
6-7 Dinner
7-8 Free time (any video games are allowed)
8-9 No electronics except the nook
9 Bedtime
Sunday
8-8 Free time, any screen time is allowed, though I try to make sure we change up what we're doing every hour or so. I aim for 4 hours of video games over that time span. This is also when we watch movies etc.
8-9 no electronics, except the nook
9 Bedtime.
Again the goal here is to provide tons of options and to let one of those options be screen time. At the same time though, not letting all free time be screen time.
As for going about enforcing it or acting on it, the best way is an honest conversation. Explain why you are setting the rules. Set them. Allow for some flexibility, but not much. And if you have no time limits today, prepare for war. Also, be prepared to listen. "I worked really hard in science today, and I find this relaxing, can I please play more?" You need to be ready for that and be willing to be a little flexible. Usually, some gentle reminders and coaching will do, but if it comes to it don't forget you're bigger. You can just take it away.
Two warnings, first, remember that kids learn by seeing. I see lots of parents going, "Why is my kid on their phone so much?" While they're on their phones. You have to find you're own path here, but when trying to set up screen time rules, try to follow them too.
Second warning, the internet and cell phones are more common today. Kids have never not had them. It's important to remember that. Cell phones, text messages, different apps, and "posting" are forms of communication. You may have run next door to talk to your friends, and your child may text for that same level of conversation. When limiting screen time, remember you are also limiting their ability to interact with others. If you make a rule to turn the phone off at a certain time, remember that means no video games, but also means no face time with grandma. Just something to keep in mind.
