ArenaNet has announced its plans to open a four hour stress test of Guild Wars 2 next week. The test is expected to run from 1PM to 5PM Eastern on Wednesday, June 27—working hours during a weekday.
It's hard to tell how ArenaNet plans to get any usable data out of the stress test when they're setting it at a period in which most people are likely to be at work.
If you're already a part of the weekend tests, you can simply update your client and log in at the time to join the stress test. The stress test will not be replacing the weekend sessions they have planned leading up to the game's release later this year.