[Fededorbprago]

as an object travels at speed it begins to gain mass, the greater the speed the greater the mass of an object. time is relevant to mass, therefore as your mass increases due to speed, time will decrease relative to the craft in comparison to earth time. as the ship decreases speed it looses mass and therefore time increases until it reaches our norm at a near static position.

as an example, the earth's shape shifts as it orbits the sun. it is not truly spherical, but in fact elongates from the horizontal to the vertical position (like bouncing a ball in slo-mo). if you were at the peak of the elongation of the earth, time would increase slighty compared to the equator of the earth due to loss of mass, this has been proven.

another example is a black hole, its mass is infinite (as far as we know), therefore it is timeless so to speak. one could stipulate that a blackhole is an object, but because its mass is infinite and timeless, we cannot see it in this dimension of time-space.

as you said, the light from a distant region was created thousands of years ago and the destination may not be there due to the timeline of light travelling, thus you find the paradox of so called time travel, is that basically it is a form of suspended animation at light speed thus preserving the ship and its contents, just like chriostasis. yes, when you return to earth thousands of years will have passed because you were in a preserved state aside of the earths timeline. technically, we do not time travel, it is "preserving time-space".

einstein realised that time and space can bend and contract. the mass of an object (such as earth) bends the time-space around it, therefore creating a specific timeline within that space. at light speed with increased mass, you contract time, slowing down will expand it.

nice question btw