Here's a random thought - if you make a game by having many nodes/choices at each step/fork/quest you could end up with a lot of material but few steps.
An example would be fleshing out detailed ways to solve the major quests by different ways using different classes, choices etc. The choices are the forks which end in nodes.
Imagine a fanning-out pattern, or at least a straight line with lots of mini-fans at each fork. That could possibly be a lot of material but the number of periods (length of game?) would be short. Compare that with a more linear game - less choices would just mean stretching the effort into a straight line - possibly more periods (straight line vs fan). Short finish but lots of replay material for the hardcore dudes? Perhaps.
If you're looking for your "40 hours" like I certainly am, the time may be in replaying the different outcomes.