Hmm. I don't know. At 15, I think it's time he started (if he hasn't already) learning how to manage his own time. I no longer limit my kids' time on electronics in that way. However, they are still required to use good manners. so, when we have family time, or are out at dinner, or at home at dinner for that matter... no electronics! It's rude! And we don't do rude at dinner. Know what I mean?
If they have homework, then the homework needs to be done before they start a movie or a game or they sit texting with friends. If homework is done, and any chores are done, fine.
What tends to happen at our house, if I notice one of the kids seems to be sitting motionless for too long with a device, is that I find things for them to do. Chores, usually. Clothes need putting away, the trash needs emptying, the rug needs to be vacuumed, the yard needs poop scooping, help empty the dishwasher, go get the mail, take out the newspaper to the recycling, study for tomorrow's quiz, practiced your musical instrument yet today? and on and on... there is always something you can suggest.
But some days, it's ok to sit and veg out with electronics a little. Really. My kids don't sit on ipods or hand held games when friends are over usually. They might get on the PS3, or watch movies, but more often than not they hang out outside walk around talking to each other, or waiting until dark to play war-games like capture the flag.
IF the grades drop, or there are disciplinary issues... then the rules change. But for a generally compliant teen who is doing what is expected, then I am not going to sit with a clock and dole out minutes/hours for electronics. In18 months (or less) my son will be off at college. If he doesn't learn to manage his time now, when is he going to learn??
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We do, however, require that phones are put away before bed. They don't go to their rooms at bedtime just to be on their device. No. Phones get plugged in overnight to charge in the public areas of the house when it is time for bed.