As it turns out, traveling through time is made possible not by human innovation, but by evolution: there are beings for whom the ability to manipulate temporality is something they're born with, like an organ- an organ that is out of space, and exists somehow only in time. The activation of this mutation seems to occur for humans sometime toward the end of the 20th century, when the first people with Extra-Temporal Abilities (ETA) begin to discover this gift, again, as it turns out: just in the nick of time.