Or planar travel where time may be inconsistent. Or dreams. Or alternate dimensions.
Or heck, just simply our own Earth. The length of a day varies based on gravitational pull, ocean levels, magnetic poles, etc. The variation for us is miniscule but over centuries or epochs it's quite significant.
Here's a fun article:
http://phys.org/news/2016-06-earth-a...tic-field.html