Rough distribution of RPG events:
- 1 hour: 250
- 2 hours: 516
- 2.5 hours: 37
- 3 hours: 274
- 3.5 hours: 44
- 4 hours: 2688
- 4.5 hours: 19
- 5 hours: 447
- 6 hours: 63
- 8 hours: 17
4 is certainly the default, but it's by no means the only way people run RPGs.
Again: if you're running a relatively small-scale event for a dozen players or less, then just run the coolest event you can't. Don't waste time trying to figure out the default or the optimal time or whatever else - if you run a cool game you'll be able to find a handful of people to come and play it.
Pick a time and duration that both works for you and the game you are trying to run. If you need 5 hours to be comfortable and not be rushed? Take it. If you want a focused 2-hour games that's in and out? Run it.
Chances are high at Gen Con you'll find enough other gamers who like the things you do the way you do that you'll be able to fill table.
Just make sure your event listing sounds as exciting as your event is going to actually be - and then tell people about it.
Gen Con LLC