To the Time tab I've added the length of the game with the expansions mixed in. To decouple expansions from investigator count, I tallied only games with 4 investigators (the majority of all games, a bit over half, are this number).
What's interesting is that every expansion makes the game shorter! I interpret this as being a combination of effects: games with expansions are more likely to have experienced players (who do not have to look up rules and who better understand victory strategies); and games with expansions are harder, and harder typically means the game ends quicker.
Another surprise is that Miskatonic and Lurker top the charts as the lengthiest single expansions, surpassing even the board expansions. I'm assuming this is because they've had the fewest plays and that players might be a bit iffy on the best strategy to win.
"All 8 expansions" is ringing in at 3.5 hours on average, which is the value I've been citing for some years as my own experience playing with all of them. Of course, this is a bit circular: that number is derived probably in a large part from the all-expansion games I've played.
Edited by Tibs, 29 March 2014 - 02:15 PM.