Here are the guidelines for the summer. I read it out to the boys last night. They weren't super happy, but resigned (helped by the fact that they had full tummies). I pointed out that we were looking for balance and if we saw them exercising 20 hours a day we'd pull them up too. That added a moment of humour and seemed to give perspective on this issue. It isn't just about electronics, it is about learning to get a balance in your life when you have a lot of freedom and few responsibilities.
I'll try to report back here on how this goes. You'll notice that there's no measurements here, I haven't said "every day" or "before you get to use your devices". Nor are there specific limits promised on internet time, that allows us to use discretion. We'll see how it goes and what revisions are necessary and how the guys rise up to meet the challenge.