“Today was Tomorrow Yesterday!”
In other words, living beings live in and experience only the present without any recourse to the past or access to the future. To simplify, the future is not a tangible commodity to be seen or experienced firsthand by means of a theoretical time travel. In the same vein, a visit to the past is not feasible by any means including the hypothetical astral travel.
Time is a relative concept not subject to quantification, experimentation or storage. It has relevance only to living beings, and therefore, shall cease to exist when life ends. However, how time operates in the realm of spirits is not known to mortals for their own good. Also, time, like distance, is inconsequential elsewhere in the universe devoid of life.
Thus, it can be safely concluded that the unsubstantiated stories related to time travel, pseudo John Titor, time machines, back-to-the-future experiments etc., are plain drivel having mere entertainment value, but without any relevance to human existence.