My kids are 6 and 9 this summer. We set a few rules this year, because otherwise they'd be asking for screen time constantly and everyone ends up unhappy. We've decided on two 1-hour blocks of screen time most days, which they earn by accomplishing a list of things (educational workbook, reading, walking the dog, etc). So far it's working out really well. They know what's expected of them, and they know when they've reached their limit for the day.
Great question, and one I know we all struggle with!! This summer, we’re trying out one hour of “free” screen time daily (for games, movies, shows, etc) which they can carry over within the week, plus an extra two hours a day for any personal hobby that might require use of a screen - like coding or writing. It’s tough to cut down screen time as much as we’d like just because use of it is so pervasive in all aspects of our lives!
I feel we are a little more relaxed about screen time over the summer. However, I do set limits and have certain requirements for the day such as chores and reading before my kids are allowed to play their ipads.