I'm not sure that WGT has made a mistake, perhaps only the different timezone use is confusing.
All WGT tournaments are in PST (UTC -8), usually from midnight to midnight.
The CDP bonus is in GMT (UTC +0).
CC tourney seem to be in CC timezone time, starting whenever they are set up.
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All of the following only refers to the game client.
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Question is, what does the game client display? I think b0geybuster got it:
All tournament times frames in the game client are time zone specific....
That is, for all timezones east of the US west coast, 12 am PST on a certain day will be some time on the next day, since we are ahead of their clock time.
In one post two cutouts of the game client were displayed, one from the west coast (PST?) and one from Great Britain. This display has only the date, and it would be logical that the tourney closing dates vary between them.
TBE nailed it partly:
The way I read things is that here in UK we get a further 7 hours on the cut off time due to GMT = PST +7 hrs.
This bunch of hours was on the 21st, correctly shown. The only misunderstanding is that we have not the whole new day but only those few "extra" hours.
OTOH, the start is on the new day in California, too, so these are the same.
For time zones behind PST, that is further west (Hawaii) the starting day should be one day earlier, while east of the Pacific we'd soon hit the international dateline - Japan and Australia and the likes count as "east of California" like us in Old Europe.