I’m guessing all ‘time’ exists simultaneously - more like a solid than a line...
Man goes around the moon comes back one second younger and since ‘man is NOT the measure of all things’ - he arrives in a different part of the solid.
Some theorize that TIME is like a rope or cable strung between two ‘endpoints’, the beginning of Time and the ending of Time.
The cable/rope itself does not move. You move along it, but in just one direction. You can move backwards but not with the current technology.......................