It took them less than 3 (three) days to rush through the raid content. That includes bosses like Malygos that are After Naxx. Also as some people say that they have rehersed all this in beta.. so they did in TBC.. It took about two weeks (I checked.) to get world first Kara clear. Naxx (v2.) took a little over two days.

But I don't like rushing myself. I think people who rush through content like that without enjoying and admiring the work put in it are fools. What gets me, is that if endgame content (until next patch months away) would have been cleared by someone this fast on any other MMO there would be tons of negative posts on it.

In the end, if you're having fun it's the only thing that matters.