Why the weekly tournament are moving 3 hours backwards every week including monthly shield tournament. Except playstrategy medleys and game medleys IE. Chess,Draughts,shogi,etc..?

The shields alternate between 12 and 18 UTC to cover more timezones. For the other two, if I had to guess, I'd say it's convenience. The weekly is shifting 3 hours so it's easier to cover timezones and to have variety. And the medleys so people who may not play on the site frequently, know at what time the medley is consistently happening.

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Then that should also move 3 hours forward. Variants medley and playstaregy medleys too