Yeah, the last tournament lasted between an hour and a half to two hours or so.
The livestream itself was just under two hours, though. You can check it out the VOD if you're curious:
http://www.youtube.com/watch?v=7etJUly3Lbk
This tournament will likely be larger. Instead of 8, it'll likely be 16 or 32 participants. That means the extra round or two will extend the tournament to maybe 3 hours total or so.
At the moment, the livestream will begin 1 hour after the first games begin, so 1:00 PM GMT-6 (12:00 PM PDT, 3:00 PM EDT, 8:00 PM BST, etc.). It will continue at least until 20-30 minutes after the final game ends (since we're going to stream that game also, obviously).
http://www.twitch.tv/Mythonian is where the stream will happen!