There's a new electronic device on the market for parents to manage how much television their children watch, and how much time they spend playing electronic games.
I'm not sure I'd take to heart the studies suggesting your child will be obese, stupid, grow a second head, and turn into a pumpkin if they watch too much telly, however you need not spend perfectly good money on a device to do what God already gave you two hands for;
switch off the box, pack it up, and return it to your child when you have sufficiently established enough trust in said child to permit them "screen time" without an electronic nanny to do your parenting for you. Very long run-on sentence (sorry) but consider your problem solved. Note, monitoring your child's activities via an electronic nanny probably won't help establish that parent/child trust bit, but it will probably get them ready for the world of work. You have to weigh the benefits, I suppose. Someday the IT person will be reading their emails, and see them surfing porn at work.
Why the devices anyway? If you can take the time to select which shows/games are appropriate and permitted for your child, isn't it simple enough to express that to them without resorting to locking devices and timers? I mean, I wanted to watch Dark Shadows as a child, but wasn't permitted. I can't imagine disobeying, and watching it anyway. My mother would have killed me. Wait, let me repeat that: my mother would have killed me. No television show would have been worth enduring listening to her scream at me for however long her stamina would permit (and she had surprisingly good stamina for screaming, what with all the heart attacks and such). No, you just didn't pull that sort of nonsense-and I seriously doubt any of my friends would have either...because their mothers would have killed them. You get the idea then? Good. Problem solved.
And if you'd please,
GET OFFA MY LAWN!