What part of game development do you work in where you can even quantify how far behind they are on schedule? When WoD Beta formally launched they had the intro experience and two leveling zones. MoP had...The Wandering Isles and the new talent system, plus a dungeon I think. Then when Jade Forest did launch, they tested it for a couple of weeks and then instantly booted everyone out and took two months to redo the entire zone.
The only things left in WoD to test are dungeons, the leveling zones, and the raiding. Everything else (such as server stability, class systems, etc) seems to be pretty set. That means it could easily take less than 3 months for them to finish.