Drysc from Blizzard posted teh following bit of information the other day about the Arena seasons. If your into the PvP thing, you should check it out.

The tournament has nothing to do with the end of the in-game season. They're completely separate events. The tournament is simply using the in-game arena standings to determine the top teams, which will then compete with each other and eventually other regions to crown the top 5v5 arena team in the world.

The cut off date where we look at the current standings and pick out the top teams is April 15, this doesn't end the in-game season, it's simply us picking the top teams as of that point to compete elsewhere. The end of the actual in-game season isn't currently set.