I think it would be a question of timing
How far back
how far forward
also present time
These measurements would have to be exact
or you could experience interdimensional overlapping which may cause bizzare effects
and could effect all dimensions past,present and future.
I don't think that time travel is possible or can ever be to any degree of accuracy because their are to many variable elements to even come up with any reasonable or workable hypothesis.
If you're serious; there are actual studies in physics that show that the future has already happened and it affects the present. There are also theories out there called m theory which says that the universe splits into different universes if you go back in time.