WGT uses PST / PDT (UTC -8 / -7) for public tournaments and the forum, and at the latter, it's visible. Just click "Active Topics" on the right - most of the time there are fresh postings.
WGT uses GMT / UTC for the continuous days played bonus (CDP) - the clock is on the game client, counting backwards.
WGT uses the local time of each CC for their internal tournaments, shown a few seconds after they've been created. It is obvious if all members are in the same time zone, but I don't know how it's handled when different zones are represented.