terms of physics, FTL travel is the most problematic part of the Star
Wars and Star Trek franchises. More irritating than sound in a vacuum,
or laser bolts that you can watch fly by at 300 m/s on the screen, FTL
travel represents a violation of everything we know about physics.
Nothing can go faster than light. That said, rather than denying this integral cornerstone of sci-fi, we choose to simply describe what it does, analyzing its behavior.
We've assumed that the mechanism of FTL travel - whatever it is - does not violate conservation of energy or momentum in real space, mostly for the purposes of determining what the peak power consumption of warp drive and hyperdrive. Aside from that, we've simply tried to describe it as consistently as possible, measuring its speed from known astronomical landmarks, distances, and times as best as we can.
Unfortunately, the data from Trek and Wars is fairly inconsistent on this. While it may seem clear at one moment in one film, your mileage will vary as you look over the whole franchise.