The Black Ops 2 Message of the Day has been updated to confirm that the next Double XP weekend for Black Ops 2 will start June 28th at 10am PT and will end July 1st at 10am PT.
Vengeance is a dish best served with Double XP, so look for it this Friday, June 28 (10am/PDT), running through Monday, July 1 (10am/PDT).
— Treyarch Studios (@Treyarch) June 25, 2013
This Double XP is in preparation for the launch of Vengeance on July 2nd on Xbox 360.
SOURCE: Black Ops 2 via @ryanwil22