This depends...
The length of time required to run a game depends hugely on the style of the group. I run quick games but my own DM runs really slow campaigns (I'm talking tortuously slow: our characters are still only 8th-level a year down the line -- and we started at 3rd).
On the other hand, I've found that if I run one game for one group, I can't guarantee the same tempo for another. I've been running a GURPS Celtic Myth game for my current group, which I'd run for a couple of friends a while back; the first two got through the adventure in a single weekend whereas my current lot have taken nearly three months for the same story.
In my own experience, I've found that most of the adventures in Dungeon can be completed in 2-4 (4-hour) sessions -- depending on how many red herrings I throw at them, how complicated the battles are or how much in-character roleplaying will be expected (all of these things slow the tempo of a game).
If you want a fast adventure, imagine how you might run a Star Wars game -- and select your adventure on that criterion. In Star Wars, the action should be relentless but not too complex (so you don't get bogged down in die rolling):
"You step into a new corridor and have to jump back from blaster fire -- there are two stormtroopers down the way with an E-Web on a tripod. You can hear the pounding of booted feet behind you -- it sounds like maybe half a dozen more coming your way ...."
