Friday June 8th is the date according to their new blog http://www.arena.net/blog/announcing-the-next-guild-wars-2-beta-weekend.
Your existing beta characters have not been deleted, and you will be able to continue right where you left off! This means that enterprising players with characters level 35 or higher will be able to test their mettle against the explorable version of the Ascalonian Catacombs dungeon!