gambit1969 is correct. They typically do the double xp (for players...not clans) at the same time the DLC launches on the consoles. So we get it when it releases on Xbox and then we will get another when it releases on PS a month later. They could have extra events anytime, but those are the times we pretty much expect it.
The next set of DLC (Devastation) is set to release on Xbox on April 3rd so the next double XP weekend should be that weekend.