To any GMs who've had a problem preventing the 15-minute workday in the past: how did the characters get away with it? Why wasn't the artifact long gone by the time they woke up?
The one campaign where it became a REALLY big problem I ran 2 different purchased adventures: Return to the Temple of Elemental Evil and Return to Maure Castle from a Dungeon magazine.
There will be spoilers about these adventures if anyone doesn't want to be spoiled, don't read further.
In RttToEE, most of the adventure takes place in a super mega dungeon divided into 5 pieces(or more depending on how you look at it), there are 4 temples for each of the 4 elements. Most of their "temples" are separated by areas of underground tunnel where neutral monsters live. There is then the Inner Fane where the leaders of the bad guys live.
The temples are mostly at war with each other. So, they would just as soon see the other temples be wiped out as help them. Also, they've been living here undiscovered by the world for many years. Their religion is banned and probably would have them hunted down in any country in the world if anyone found out about them. Plus, this location is a holy site to their god.
So, the PCs would teleport in and attack one of the temples. They'd fight 1 or 2 encounters, then teleport or run out. The temple in question would lose half their fighting power, given that most of the temples only had about 30-40 members, and each fight had 5-10 of the members in it. They didn't warn the other temples because they didn't want to seem weak.
The neutral monsters never found out about the attacks because they weren't affiliated with any of the temples and most of them had animal intelligence.
The Inner Fane explicitly didn't care about what happened to the temples since they were pitting all of their followers against each other on purpose and wanted to use the temples as a buffer to keep the PCs occupied while they completed their ritual to free their imprisoned god, who would then destroy the world and remake it in his image. He was the most powerful of all the gods and likely would be able to do it.
You may ask, if the PCs kept teleporting out after each encounter, why didn't the ritual finish, thus destroying the world? Twofold: The adventure didn't specify how much time the ritual took to complete, but implied that seasons might change over the course of the game while the ritual is performed. It basically said "It's not a good idea to destroy the whole game world, so it takes as long as it needs to for the adventurers to complete their mission." Plus, with the PCs having no way to know how long the ritual would take to complete, just having the world end one day and saying "So sorry, the world ended since it took you over 2 months to stop the bad guys" wouldn't have been fun for anyone, even me.
Then, after completing that adventure, they went on to Return to Castle Maure. This adventure is a matter of exploring a strange dungeon that has been abandoned for over 100 years. There's no particular goal. I just told the PCs to find an item somewhere inside of it, but it wasn't life or death, just someone paying them to find the item because it was rare.
All of the monsters were either insane, undead without intelligence, or golems without intelligence. With a couple of monsters that had some intelligence on the bottom levels of the dungeons who never went above their levels...some of which who hadn't left their rooms in over 100 years.
The PCs teleported in, killed one room of monsters, and teleported out. They explored a room or two a day.
I've found that 90% or more of the adventures I've run don't have a hard and fast time limit on them. Partially because it's more fun for me if the PCs arrive in the nick of time to stop the villain so I don't set hard and fast times for things. I know a lot of other people say they put a lot of time limits on things...but I don't.