Salvation is contingent upon location

This is a very hypothetical situation but plausible to occur which has potential interaction with salvation.

By location I'm referring to distances incredibly far away from Earth. Here is the scenario:

In the near future, say the year 2500, wormhole technology becomes a reality, crossing light-years of distance instantly by bending space instead of traveling through it. A Christian traveler and their spouse travel 3000 light-years from earth through this wormhole to start a new life together. They would travel to a location where it would still be another 500 years until Jesus died on the cross relative from that new location.

They then have children. Since it'll be another 500 years until the cross event occurs, the children would not be able to receive salvation and would still operate under the old covenant.

One could argue that at the moment Jesus died on Earth, salvation instantly spread throughout the universe but that would also mean that for those people living 3000 light-years away experience salvation 500 years before Jesus's death and resurrection from their perspective which is paradoxical, effect would proceed cause.

So if my understanding of physics and salvation are correct, one must currently reside within approximately 2000 light-years of earth to receive salvation through Jesus. Or in other words Salvation spreads at the speed of light.

I'm sure there's something I'm missing but I don't see any other solution in this scenario. I welcome any other viewpoint or solution to the problem.