I am quoting directly from the manual here:
The Clock Options Screen lets you turn on and off a clock to time how long you've been playing, as well as set an alarm to let you know when you should stop playing and go to work. Or eat.
Of course, they had the fabulous ad campaign at civanon.org which appears to be down (overwhelmed or ended, I'm not sure.) I'm happy to announce that the game seems no less addictive and I made good use of my extra hour this weekend. In particular, many of the more tedious actions have been removed, automated or at least present you with more choices so that it's not A, B, repeat.
So if I vanish for a while...yeah, you know where I am. I just have to get my civilization to research Gunpowder...