There wouldn't be much difference if we added this - if you all sign up at different times, then the clock starts automatically at the scheduled time but one of you isn't on, then that's bad for the one person...much better to PM everyone, say "be online at 2pm on the 3rd" and then start when you know everyone is there...are you always within 5 minutes of on time??? because it you're not then the game would start without you...our servers are always on time
This will be made easier once we get our friends list integrated into the site so you can see who is online at any given time.