[3.5] Planning one-session adventures

[Salanmander]

I'm about to start DMing a side game for my current D&D group, and one of the things I need to do is have it be fairly episodic. I can do that plot wise, but I'm a little worried about making sure that each session reaches its conclusion in a reasonable amount of time.

So Playground, when you need to plan a single-session adventure, how do you maximize the chance of it finishing in a roughly pre-determined amount of time?

[AslanCross]

Back when I started, the most I had was a 1.5-hour session every week. This was pretty sufficient for an "interaction-single combat encounter-cliffhanger" episode format.

[Salanmander]

I'd be looking at probably 3-4 hours of play time, and needing to get back to a spot that people can freely join/leave without it being weird. My biggest objective is to have a variety of ways the players could approach the situation, I really want to avoid "here's your staged combat of the week" situations.

[Chainsaw Hobbit]

About two encounters or one big one is perfect. This leaves time for a bit of exploration and setting the stage.