The dev team notes that at the beginning (and I presume the end) of the event, there will be a brief interruption to setup and turn off the Double XP
"Please be advised that a brief reboot downtime lasting less than a minute will take place in order to facilitate this first ever double XP weekend event. We apologize for any inconvenience."
- Double XP Weekend! on Official MWOMercs.com News (Link below)