Which timelapse intervals should I use?

Ever wondered how fast you should be shooting photos? What if the clouds are faster than usual? Or slower? How do you shoot timelapses of water? How many photos do you want to take for a sunrise or sunset timelapse?
Clouds, depending on speed, I'd shoot at around 3 seconds interval.
Water, as fast as possible. You don't want it to look choppy.
Sunset or sunrise: around 8 seconds. Not too fast, not too slow.