1) There are five dimensions: three of space and two of time. The second temporal dimension is called "metatime". Time travel can move information backwards in time, not metatime. That would be metatimetravel, which doesn't exist.
2) For every object that exists, that object travels through time and metatime at the same rate. Relativistic effects on an object's motion through time have a corresponding effect on its motion through metatime.
3) If an event within a timeline changes that timeline's past, the timeline branches. The branch begins at the time where the variant event occurs and at the metatime of the event that caused it.
4) If two timelines are very similar, or sufficient external pressure is placed upon them, the timelines merge. The new timeline "jumps" in metatime to be coterminous with the meta-later of the merged timelines.
5) If a timeline which caused events in other timelines "jumps" as a result of a merge, those other timelines may now contain events whose causes lie in the metafuture. Such events are simply treated as having no cause. While this does not inherently disrupt the timeline, those events become Etamnanki incursion loci.
6) If an event contradicts its own cause, the result is a cycle in metatime. Every other iteration does or does not contain the paradoxical event, as appropriate. Each iteration constitutes a forked timeline.