Absolute Location

If the speed of light is constant, that means that it is not relative to the movement and motion through the universe. That means it must be constant with it’s location in space.

So… there must be absolute location in space.

Therefore, time travel on a planet is impossible due to the fact that heavenly bodies are constantly moving through space and time.

The only way to travel through time, would be to get a spaceship and go to an absolute location is space, but that would pose some serious issues, due to the fact that the planets and solar systems would be moving relative to you.