I think that's something that would be a lot of fun, and add something more to the PvE side of the game. It would also encourage more offensive builds, not just the farming invinci-monk all over.
Now, this could be done in various ways.
1. There is a town/outpost somewhere with one or more explorable areas around it, just like any other town. But when you enter an area, a timer starts ticking, a 60 minute one for example. (If there are more than one town/area like this, the timers could vary in lenght) So you can only spend a finite amount of time in this area. Then you just run around as usual, and do quests that you get from NPC:s either in the town or stationated out in the timer'ed area. Once the timer hits zero, you and your party are teleported back to the town, regardless if you've completed any quests or not.
2. You get the quests from NPC:s stationated in explorable areas. Once you've finished talking to the NPC and have gotten the quest, the timer starts. The problem is see with this way though is that when you get a quest from an NPC only you get it, not your entire party. Therefore, if done this way, the entire party would need to get the quest in their log if one member gets it, so that the timer would be the same for the whole party.
Personally, I like the first way better. It adds the challenge of completing multiple quests during the time limit, and overall I think this way would be the most convenient and fun. So what do you think, would time limits be a good thing to add to some future explorable areas?