The problem with the ETH is that popular sc-fi renditions of time travel are not possible. For example, a time traveler from the future can not alter his or her own history. At best, it may be plausible for a time traveler to seem to return to a point in the past and initiate a new timeline. In this new timeline, change happens independent of the time traveler's original timeline, thereby avoiding temporal paradoxes. However this approach isn't really time travel. What is actually happening is that the larger construct that facilitates the existence of spacetime, sometimes referred to as the multiverse, is allowing the time traveler to access a historical record of his or her own timeline and run it in a separate spacetime environment; or what would be popularly referred to as a parallel universe.
From the point of view of those in the time traveler's original spacetime, the time traveler would simply vanish and life would carry on as usual. Meanwhile, from the point of view of the time traveler, he or she will seem to have been transported back in time. But from the objective point of view of an observer outside of both spacetime environments, the time traveler will neither have vanished nor traveled backward in time. This is all logically consistent and possible within a computational or informational model of the universe. These concepts evolved from holographic theories of the universe and digital physics, both of which emerged during the late 1960s and early 1970s. Computational and informational models of the universe offer explanations for peculiar phenomena in both hard science and the paranormal.
With respect to ufology and the ETH, we can hypothesize that some UFOs are devices capable of accessing parallel and nearly identical universes that are at different stages of evolution, giving the impression of time travel to the UFO occupants.