Einstein never said time has two vectors. It has a magnitude only—it can be sped up or slowed down, but not reversed. You can go into the future, but not the past, by using relativistic time dilation. To have gone into the future and return again violates special relativity. I think Einstein would disagree with that.
The MAIN problem with time travel is motion.
Nothing stands still.
Everything in the Universe is moving. Any given second, or microsecond, you, the Earth, the Sun, the Milky Way Galaxy and every other object in the universe is moving.
Let’s say that you just invented a ‘for real Time Machine’.
You step into it, set it for some particular time, forward or backward, it doesn’t matter which, and turn it on.
)Poof!( you disappear immediately from this ‘time’.
Suddenly you reappear at the designated time you set and immediately die.
You find that at the time you set, the Earth was not there, and you are in a vacuum of space and no chance to get back.............