If you want a good explanation of the history of speed and how it currently works check this thread:
https://forums.galaxy-of-heroes.starwars.ea.com/discussion/58474/a-cavemans-guide-to-speed-mechanics#latest
If you like relativity, and want a deeper look, check out this thread. There are a few different ways that speed can be modeled to make it easy to understand, there are examples in this thread. No matter how you model it, once tm manipulation occurs, you must look at it relativisticly.
https://forums.galaxy-of-heroes.starwars.ea.com/discussion/61800/a-cavemans-theory-on-time-travel-gravity-wells-and-the-relativistic-effects-of-time-in-swgoh/p1
