Where to watch:
On your Xbox.
On Xbox.com: http://www.xbox.com/en-US/hub/reveal
From Major Nelson:
#XboxReveal Day: Where to watch
Watch the main event today at 1p ET/10a PT/17:00 GMT via the live global stream that will be available on Xbox LIVE and Xbox.com. If you are in the US or Canada, you can also watch the broadcast on Spike TV.
Note: The Xbox.com version should be viewable on most mobile devices.
If you have a If you have a Windows Phone 8, download the free Live Event Player to view watch the stream.
The full show will be available later in the day for viewing via video on demand on Xbox.com and Xbox LIVE.
PLUS later today at 3p ET/12n PT/19:00 GMT I am hosting a special #XbxoReveal recap show that will ONLY be streamed on Twitch.tv During this time I’ll be joined by guests who will go into more detail about our #XboxReveal announcements. This will be available later in the day on Twitch.tv for playback as well.
If you can’t join us for the live event, you can follow me on Twitter where I’ll be sharing the news throughout the day.
From polygon's page (thank you spacer!)
Sydney: 3 a.m. [Wednesday]
Tokyo: 2 a.m. [Wednesday]
London: 6 p.m.
New York: 1 p.m
Chicago: 12 p.m.
Los Angeles: 10 a.m.
Honolulu: 7 a.m.