QuoteWhile testing continues and a delay could possibly change these dates, we are currently planning to start Season 3 on November 20 once the realms come back up from their weekly maintenance. This means that Season 2 will come to a close when the realms come down for maintenance on November 20. During that maintenance the final standings are taken and the end of season rewards are distributed.
The start date for Season 3 is purposefully planned to be one week later than the release of patch 2.3, which is currently scheduled for November 13. We will be closely monitoring the testing of the 2.3 patch, and if it looks like it won’t make the November 13 date, we will announce a delay.
From http://forums.worldofwarcraft.com/thread.html?topicId=2766101883&sid=1 (This topic also has a short Q&A and is worth checking)
Edit:
Most notable Q&A:
QuoteQ: What happens to my rating when Season 2 ends?
A: Ratings for all teams are reset to the default 1500 for the new season. You still keep your arena points though, they aren’t diminished or removed.
Thanks for that Bastet, I probably wouldn't have seen it other-wise, lol.