Your mass remains the same regardless of your location. Your weight will change depending on your location.
You will weigh less on the moon than on the Earth. You mass doesn't change however.

Time travel to the past is not possible. Time and space are intrinsically intertwined, referred to as space-time. You can't have one without the other. You can't have negative length, same is true for time. You can't have negative time.
If you walk 10 Km in one direction, then turn back and walk back to your starting point, you will have walked 20 Km, not zero.
Time is also measured in the positive direction.
The speed of light is the universal speed limit. Nothing with mass can achieve the speed if light. Light had no mass. Nor does electro-magnetic waves, they travel at the speed of light. Time halts at the speed of light. It is not possible to go faster than the speed of light, so time travel to the past is also impossible.

What? No tome in space? Time and space are intertwined and inseparable. Time exists everywhere.
The faster you go, the slower time goes for you. If you were in a spaceship going near the speed of light, time would pass for you very slowly. You would not feel it. One second to you will tick off as one second.
Someone observing you would see one second on your clock ticking by extremely slowly. Time will have passed outside your spaceship very fast compared to time inside the ship.
You will have hardly aged compared to the people you knew on earth.
Time is relative to the motion of the individual.

I enjoy seeing guys in long johns. I'd like to have a bud who would hang out in them with me.

You're cute. Get out there. Meet people.

I'll take it. There is nothing supernatural about them.