Actually XBL is up. I've been logged on all night.
I dug this up on the Xbox.com forums. This is what the release times look like:
It releases at
2am PST: Microsoft is based in Washington state and that is what time they are hitting the button
3am MST
4am CST
5am EST
10am UTC UTC is +5 hours ahead of EST so it will release there at
http://forums.xbox.com/24121761/ShowPost.aspx
This is for people that love countdowns: