With a full group: 45 minutes or so With 2 other people: 1 hour to 1 and a half hours As a pair: About 1 and a half hour to 2 hours Solo: About roughly 2 to 2 and a half hours.
The entire dungeon took us an hour and half. It would not have taken that long but a few of us had wrong decks equipped for the first fight.
As for Young Morganthe, it took us (2 fire wizards, one balance, and one ice) a half hour. During the entire battle she only cast one woolly mammoth, that was at the very beginning. I do not know if this was a fluke, or if it was the fact we used stun shields at the very beginning. (I am sure it was a fluke and Morganthe was just too stunned at our awesomeness to use more than one woolly mammoth).
