I limit my kids to about an hour or two a day of total television viewing. I don't like them sitting inactively in front of the TV all the time and doing nothing later that day. I like them to be active and outside a lot.
I usually don't limit my kids to the time that they watch TV. They basically do it themselves. I rarely ever see them hanging out in the living room, or in the den. They are always out in the backyard exploring.