That’s not really true. First, if you can invent time travel you can probably do the math to calculate positions of objects. Second, even if you do need a beacon, you could use something that already exists. For example, radio waves. Earth has been shooting off radio waves for a fair amount of time now. That could be used as a beacon. Also, you could do something like having your time machine do small jumps, check it’s relative position, then adjust. This would solve just about every issue.