There will be no raids available to players when Mists of Pandaria is released on Sept.25, 2012
Blizzard announced that the first tier of raids in Mists of Pandaria will have a staggered release. A single raid will be released one week after the launch of the expansion, Mogu'shan Vaults, and the raid finder version of that raid won't be available for another week after that. Nothing will change regarding the release of heroic modes, which will be available for the following lockout after players complete the raid on normal mode.
Tier 14's other two raids, Heart of Fear and Terrace of Endless Spring, will be released four weeks after the release of Mogu'shan Vaults. The full details of this announcement are outlined in the blue post below.
Follow the link below to read up on Mogu'shan Vaults http://us.battle.net/wow/en/zone/mogushan-vaults/