
Re: How long will running a published adventure take?
I'm not a fan of counting on this. I have been at cons where the game ran over and I had another event, but the rest of the group played on. In general, I think it is very unsatisfying for a game not to resolve in its scheduled slot. Here is my advice for getting it to do so.
1. Trim as much of the explication out as you can. Anything non-essential or too fussy must go! Despite what you may think, nobody likes to sit and listen to you explain the world, the scenario, or have a dialogue with yourself in-character(s). This means you have to jettison some subtlety in favor of communicating clearly what the plot hooks are. Don't waste time asking questions like "Do you accept the quest?" Just state it "As servants of the king, you have accepted this quest." See my above advice along the same lines, why start at the tavern when you can start at the dungeon door, or even in the first "room?"
2. Include an optional encounter. This encounter can be switched out for reasons of time or because the party is too banged up to endure it without compromising their chance to "win" the scenario. Make the scenario some kind of fun puzzle or fight scene on unique terrain (or with monsters that have unusual tactics). This will make it memorable, should you use it. (It shouldn't feel like filler.) At the same time, make sure it fits in with your theme but doesn't contain anything necessary, or at least not anything you can't deliver in another way. For instance, the princess has a key that the party needs. In the optional scene she is imprisoned in a tower guarded by a small group of flying harpies with befouled talons. (They are disgusting things that fling poo and their scratches cause disease. They attack from above, darting in and out.) If you don't have time for this scene, have them simply find the princess/key by some other means at the end of the previous encounter. Or better yet, make the key non-essential. It locks a door to great treasure, but the door can also be defeated by cutting off the evil sorcerer's hand and turning the knob with it (or somehow forcing him to turn the knob with his own hand).
3. Pacing! Watch your time. Don't let players get caught up in lengthy planning sessions. Put out a sand-timer if you must and tell them they have to act when the timer runs out. If I'm at a house con, I will sometimes just say "I'm going to the bathroom to take a piss. When I get back you have to have an action ready." If you have a three-fight scenario, make sure you have an hour or more to do the final battle. If you can leave 10 minutes at the end you should. People love to sit around and debrief a little after the game. It makes for a better overall experience.
One more word on pacing. It's better to rush the group early in the game than at the end or to not finish on time! So start managing your clock right away. Don't "saunter" to the mid-point and then check the clock and shift gears. BURN RUBBER BABY!