I wouldn't a mind a timed quest, have one that is either quite strict, or have several that are very generous. Too often in RPGs we are told to "hurry before the bad guy takes over the world" and then we cruise down to the mall and buy some stuff, check out the local hotties, rescue some captured merchants, get a cat out of a tree, and then cover the land with a fine tooth comb looting before we even reach the bad guy's hideout. In the mean time the bad guy has sat on his bum and only remembered that he was meant to be taking over the world five minutes before you arrived.
I'd rather have a generous time limit, (for example, one real hour to get from Aleroth to the Blue Boar Inn (near the farmlands)) so that you do have a chance to explore and prepare, but not so much that you can simply abuse the storyline. This would only be for key quests and, at the developer's descression, you may be able to go back over the ground you covered to finish off looting. But while the quest is active, you have to manage your time and resources as opposed to reaping every possible benefit.
