When we think about teleportation, there’s always someone talking about how you should take into account the earth and the sun moving through space. Let’s step back a little (not so much) what if the galaxy we’re currently in is rotating really really fast around another, bigger, still unknown, spacial object?
Earth itself is moving around the sun at about100,000 km/h and the sun is traveling through the galaxy st about 1 million km/h.
So if Marty went back/forward just one hour then he’d be about 1,100,000 kilometers away from Earth in space (or 900,000 kilometers, depending on the orbital direction of Earth relative to the sun’s direction of travel).
And then there’s the motion and speed of the Milkyway itself.
This is all assuming that the layout of the underlying fabric of spacetime is absolute (which it seems to be, outside of expansion).