I'll tell you what I allow, but my son is 5, and won't start school until fall.
He does have a TV in his room, but we don't have cable hooked up to it, so all it's good for is watching movies. He hasn't watched a movie in weeks, but I don't mind letting him watch when he wants, generally. If he asked every day, it might be a different story. With the rest of the TVs in the house, we have one on top of the fridge, which is visible from the dining room table. That is generally on all the time, but rarely does he sit and watch it. I turn Disney on in the mornings, other than that, it's usually on either NBC or ABC. We usually watch the local news during dinner.
If the kids are playing in the basement while I'm making dinner or something, I'll turn the TV down there to PBS. The younger one doesn't sit and watch, though, and usually Owen doesn't either.
The only friend Owen has right now (other than the kids at the gym child care) is a girl across the street, and I'm pretty sure she doesn't have TV in her room, so it's not much of an issue.
I hate to say it, but if that comes up in the future, I'll likely resort to the old standby: "I'm not so-and-so's mom, this is *my* house, and what I say goes," or something along those lines. I'm SO turning into my mother already
As far as allowing them 30 minutes per night, what if you got a timer to plug the TV into? Then just program it for 30 minutes, when time's up, the TV shuts off (there are things that can do this, right?). Tell them if they don't like it, no TV the next night. I might just be mean, though
Edit: As far as video games go, the "baby" is nearly two, so that's a non-issue. With the older one, he has games on "his" computer that he can play, but he must ask first, and I don't always let him play. I just got him two games for the Playstation, but found out after hubby tried that you can't play PS2 games on PS3
So we *may* buy a used PS2 to hook up in his room, but it'll be the same as with the movies. It won't be that he can go play whenever he wants.