The Best Windows Command, evah

So, the kids are fighting over the pc upstairs. "Dad, tell him, he's hogging it. He's been on there for hours"
You reply with "Let your sister on or the PC goes off."
Your son then replies "but Dad, I've only been on it 5 minutes. She's lying"
"Am not," comes a voice.
"OK then," you decide, "the PC goes off."

For years I've wanted a way to control how long John's on the PC. The rules are 1 hour on a school night, 2 hours on a weekend. That might sound harsh, but when he can do that, I'm happy for him to use it more, as and when he needs to. There are a few programs out there, not free, that allow you to control your kids. I was thinking about writing one when I thought I'd have a play with the windows command "shutdown." In the example above, I could just type "shutdown -m //john -t10" and it would shutdown in 10 seconds, much to his dismay. I have now included the line "shutdown -t3600" into his startup group, so he gets an hour when he first turns on the pc. Yes, he can just reboot, but he hasn't found that out yet. He also hasn't found out that he can just type "shutdown -a" to abort it, but in the meantime he's getting his playing on the pc tempered.