Time travel isn’t actually a matter of bending space-time. There are no wormholes here, just what amounts to the world’s most technological box. It doesn’t go anywhere, or in fact DO anything. The superfluid shell is incredibly noisy, and steam billows off it impressively, but for all the exuberant arm wavings of the media-scientists, all the “dampening-this,” “isolation-that” and “the-other milimeters thick,” it is only a box, doing what we all had assumed boxes did perfectly well up until now.
It just contains things. But it does it completely and perfectly, so there was no way to tell the state of anything inside. More importantly, there is no way to tell the state of anything outside. For us it boxes him in, but for him, it boxes in the universe. Step inside, close the universe up in a box, and there is no possible way to tell when or where is inside.
Until you open the box of course.
This would all be extremely clever and groundbreaking, except that the only thing we ever find inside are dead cats.