All Mists of Pandaria WoW realms will undergo 1-hour maintenance this week, with no new content being added to the game.
U.S. Realms Maintenance – September 30th
Americas servers will undergo maintenance at 7:00 AM PDT and are expected to be unavailable for approximately 1 hour, until 8:00 AM PDT.
E.U. Realms Maintenance – October 1st
European servers will undergo maintenance at 03:00 CEST and are expected to be unavailable for approximately 1 hour, until 04:00 CEST.
Source: Weekly Maintenance Schedule