My 5-man team on Mag took right at about 18days, 19hours.

My 4-man shadow priest team took right around 20 days.

My 4-man fire/arcane mage team was just under 17 days.

The mage team did not level anything but gathering professions and enchanting to d/e drops. The priests all had gathering, enchanting and about 350 tailoring before I stopped. The priest+locks have 300 tailoring x5, 350 enchanting and 240 mining, 301 herbalism and about 200 skinning at the time I hit 70.

[edit] To answer your question about how I leveled, I did straight quests minus the really annoying collection ones (I did do most of the collection quests) up through 33. At 33, I farmed SM for drops from doan and the cathedral. I ran every instance at level when the quests became available, with the exception of BRD as I just despise that instance. Tried Stratholme at 57 but was just too tedious. Was easy mode at 60. Tried Hellfire Ramparts at 62 but wiped on nazan due to fire breath and having to move all the time to avoid the pools of fire. Ran it again at 68 and was easy mode.

Once I got to 58, I went to outlands.

For anyone under 60, I would definitely do all the old world quests you could before going to outlands. The quest XP is awesome, with the dungeon quests in scholomance/stratholme generating 15k XP per quest versus the 6k each they used to give.