Bornakk posted a tentative date for the announced end of Arena Season 5, indicating that the season can end "as early as April 14" or a week after. It should be noted that the first four Arena seasons had no breaks in between, with one season beginning immediately after the last ended. Arena seasons were only suspended upon the release of Patch 3.0 leading up to Wrath of the Lich King, with the first season of Level 80 Arena play beginning on December 16. This time around, however, Bornakk makes it clear that the next Arena season will not begin immediately but have at least a one week break before Season 6 begins.
This should also be taken as an indication of when Patch 3.1 will be released. Blizzard has stated that they plan to unleash Season 6 almost simultaneously with the new raid content, so if Season 5 ends within two or three weeks, it should be expected that Patch 3.1 is just around the corner. It might even come sooner rather than later, as Blizzard has noted that Season 5 would "end with or shortly after" Patch 3.1 goes live. All of the necessary files such as Season 6 items are contained in the patch, so this only makes sense.
Bornakk reminds all players who feel they will be eligible for end of season rewards, such as titles and the Deadly Gladiator's Frostwyrm, should refrain from transfering their characters to another realm until after Season 5 ends (or until rewards have been handed out to be safe). During the break between seasons, all ranked matches will be disabled and all Arena points and ratings will be wiped [EDIT: Arena points and ratings will continue to be available during the one week break to allow players to spend their points, but will be wiped when Season 6 begins.]. However, players will retain their matchmaking ratings and Honor points.