It depends on the kind of party you're playing with, as well... I'm currently soloing a solo blade, and it took me 45 (!) in-game days to get out of Irenicus' dungeon. Why, you ask? I overlooked the part that a single rest to get fully healed took 15 (!) days, so all of this time, Irenicus and Imoen were waiting for me outside to begin their little sketch. Hope they didn't catch a nasty cold.
And it also depends on the number of quests you want to do, of course. If you're playing really straightforward and don't do any quests that have nothing to do with the final plot, you could go through BG2 in a lot less time. I've heard about people finishing the game in 20 in-game days or something along those lines. [img]smile.gif[/img]