Time-travel theories are pretty extremely hypothetical as of now. So. Yeah. Little to say about that. It might in theory work in accordance with the laws of relativity. But hey. It might also not work. Singularities and worm-hole shit are a bitch.

As for speed of light. It is speed of light. It is awesome.

There is no real reason to think Einstein is wrong, at the moment. Besides that, light is awesome. Especially strobe-lights that make everything look funky.