"As part of a new marketing blitz to promote the Xbox 360 as a "family friendly" video game console, Microsoft on Wednesday rolled out a new feature called Family Timer, which will show up in the Family Settings Screen. The Timer will let parents limit the number of hours their kids can play the Xbox on a daily or weekly basis. When the time limit is reached, the console will automatically shut off, ostensibly after saving the game."
http://www.betanews.com/article/New_Parental_Controls_Limit_Xbox_Time/1194467562