How about we set some par completion times for various quests?
To kick off, I suggest that 3 minutes is a good amount of time to complete the standard Quest for Gems, while 2 minutes is more challenging.
5 mins medium, 3 mins hard for The Lost Book of the Gnome King
5 mins is good for The Dungeon of Death, I think.
The Ancient Wand of Death can take anywhere between 30 seconds and several minutes, depending on where the wand is. This isn't a good one to play as a single player quest.
Also a lot depends on luck, of course. Finding a quickness potion makes a big difference.