Let's assume it really involves <i>Brawl</i>. If this is true, then chances are, today's update will be filler (or at least, completely unrelated to this announcement), and tomorrow's update will be related to it - much like how Sonic's announcement came at that show of Nintendo's first, THEN went up on the Dojo.
But, seriously, this soon? They really can't be playing all their cards so early... I mean, the game's a million seller either way, but certainly they'd like to keep the Dojo running for as long as possible between now and January/February?
To answer your question, though, it updates at 3AM EST, 12AM PST, 8AM GMT, etc.