Fifteen minutes is the optimal amount of time for an MMO quest or activity. This is one of the guidelines to Cryptic's Neverwinter Foundry, and while I initially scoffed at such a low number I am now seeing just how right they are especially when comparing it to other online games. Casual gamers play in small chunks of time, and in that chunk they have to be able to do something they feel is rewarding, or at least get one step closer to some goal.
The main problem stems from the fact that there is no individual "save" feature in MMOs, and really - I don't know how you'd implement one to begin with. A solo game you can usually start and stop at your leisure, just like table top games - and more importantly you can continue where you left off when you decide to resume (though that would be tricky with more complicated setups like Arkham Horror or a Warhammer 40k skirmish unless you left the table as is).
In comparison, it really "burns" when you undertake something that takes so long then come up empty: Failing at the last boss of a long dungeon run, or losing connection in GW2's SAB Tribulation mode, or being defeated by Tequatl (I imagine. Haven't bothered waiting to fight him). Each of those have to be restarted from scratch if you want to try again and for someone time poor, that would be extra annoying - especially if there were alternative shorter activities they could have done instead.
I imagine that's the main problem with my first "spacious" quest. It starts in a tavern, you can talk to everyone (though you don't have to), there's a little bit of puzzle solving and a fair bit of exploration before any combat even begins. People look at the average time of one hour and simply skip it for a faster run through something (or a few "somethings") else. Well, I've learned my lesson. My second foundry quest is coming together nicely and is going to be more "condensed" than I originally planned and hopefully will only run to the 15-20 minute mark. The story will still be there, but there'll be less fluff. Should be interesting to see how well it does in comparison.
If you play Neverwinter Online and want to try my first foundry quest (despite the length) it is:
One Step to Darkness [NW-DNJC9SK7A]
You'll probably need to use the short-code (NW-DNJC9SK7A) without the brackets in a few of the tabs before you can find it. I always appreciate more play throughs and feedback!