With my kids, I rarely limit computer time, but I do have a bartering system. They have to do equal time of something educational to something randomly fun. That said, my kids rarely come home before 4 PM, 5 PM on days when they stay at school for a club, and dinner is at 6, showers at 8. They have to fit all their homework in that time as well...so there is a limit to what they can do during the week.