So I made my own riff on the Chrono-Crone idea. Here it is.
If you move any of the hands on the water clock, time stops for everyone except those in the cabin. Your surroundings darken, the outside world seems to vanish into all-consuming darkness, and from a glowing blue-white doorway that wasn't there before (and yet was always there) emerges Ananke, Queen of Inexorable Dust. She is a gaunt, transparent, gauze-like humanoid figure with a voice that simultaneously reminds one of the whispering of a moth's wings and the roar of an angry ocean of liquid time. She appears powdery or blurry, and seems to vibrate in place so that you cannot make out any facial features, or much of any features, really. She will ask you and anyone else in the cabin, one by one, if you want to travel through time, and if so, to when.
If you say no, Ananke will be displeased that you have wasted her time, for even though she has an infinite amount of it, she values every instant. You will feel this displeasure in the form of a wave of rapid and inconsistent aging across your body. You will take half of your current HP in damage and suddenly become very hungry, thirsty, and tired. You must also make a Save vs. Magic; failure means you lose 2,000 experience points and magically age by 1d10 years. EDIT: In the comments below, Yora convinced me to change this to 1d10+10 years so the effect would be more noticeable, important, and dramatic. It's Death Frost Doom, so there's little reason to hold back.
If you say yes, Ananke will name a price. It will be something that will hurt you a great deal. Here are some examples:
- Every magic item you own.
- The last 1d4 years of your memory.
- The life of a loved one.
- The ability to sense the passage of time.
- Gaining an allergy to silver and gold.
- Gaining a severe phobia of something you commonly encounter.
- Lowering one or more ability scores to 3.
- The ability to sleep soundly.
- A language in which you are fluent.
- All but one point in one or more skills.
- The ability to read.
- Half of the XP you will ever gain.
If you do not agree to the price, see the bit about saying "no" above.
Once everyone has decided, Ananke will leave through the glowing doorway, your surroundings will return to normal (if you are still present in the current era), and the flow of time around you will resumes its normal pace.
No matter what happens, from the point of view of anyone outside of the cabin, nothing happened when you moved the hands of the clock, aside from you vanishing (if you said yes) or suffering the wrath of Ananke (if you said no), with either occurring in the blink of an eye, and the appropriate effects happening to everyone in the cabin simultaneously.