NO SUBJECT

I need to leave for two weeks on vacation (be back on October 21st). I don't know how to turn on vacation mode.

You don't have to turn it on, it goes automatically (also see the FAQ):
"If the clock of a certain player on one of his games gets to 0, a day of vacation will be triggered. This means that all games of that player get 24 hours extra time. Each player has 20 vacation days. "

It might be nice if you change your displayname to 'Rudolf (on vacation)' or something like that, to inform your opponents about your vacation. You can change it via [Loging/New user]->[Edit user profile].---- Enjoy your vacation!~

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