Source: twitter
Complete info as posted by Arena.net on the official GW2 Facebook page:
Happy weekend, everyone!
We will be conducting a stress test TOMORROW Sunday, August 12 from 11:00 AM PACIFIC Time to 12:00 Noon PACIFIC Time.
REMEMBER: We will be actively working on the game during the event, so you might experience connectivity problems or discover features that are not working as designed.
Any issues you experience are a result of the rigorous conditions of the stress test, and are in no way representative of the state of the game at launch.
By participating in this stress test, you’re helping us make Guild Wars 2 a better game. Thanks for your cooperation—we’ll see you in-game!
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Please note:
* The stress test is open to anyone who has pre-purchased Guild Wars 2.
* Characters will not be wiped from the previous Stress Test.
In short: it will be a one-hour stress test (11:00-12:00 Pacific time). Not much, but it's something. I'll probably be there.