Oh, I know what caused time to get messed up, at least partially.
There are 8 planes in my setting's multiverse, sorta like a solar system. They orbit the sun.
Fire - Like Mercury.
Air - Like Venus.
Life - Like Earth. This plane has been partitioned upon itself, so that part of it, the moon, serves as the plane of dreams, an aspect of life.
Water - Like Mars.
Earth - Like the Asteroid Belt.
Space - Like Saturn.
Time - Like the rings of Saturn.
Death - Like Pluto. This plane has also been partitioned upon itself, so that part of it, a tiny moon, serves as the plane of ruins. The rest of the multiverse is sealed from this planar system by the plane of ruins.
At the end of this current campaign, the villain is going to try to release something powerful from beyond the plane of ruins, and he'll do it in a desperate fight with the PCs on the plane of time. Doing so will sunder the ring that is the plane of time, and all the timelines will be separated from each other.