An idea and alternative interpretation of events.
Our universe exists in the 4 dimensions of time. With the big bang we were effectively sent out in one of those dimensions at the speed of light which has been constantly slowing down.
The distant effects look as though things are speeding up, but they are just taking the same absolute. Our normal situation is as a mass which slows down according to size the fast speed we are going, proportional to the mass as a drag effect on that dimension of time. The drag effect is gravity, the greater there is the greater the slowing down of time. Movement is in one or more directions in the dimensions of time, which cuts into it and reduces it according to the maximum the faster you go. So you have mass, through the drag effect being experienced as gravity slowing down perceived time by the observer, but not the person with the mass and speed in any direction slowing down the time by the observer, but not the person moving in those dimensions. You might almost say that gravity and movement is equivalent to a negative time in this respect.
Time is possibly digital and particular, so things in the small scale may have the boundary cumulative effects of larger mass items which can cause appreciable drag. It would be proximity to mass which may change the effects. If there is such a particle as a chronon it would be the saturation level available to sub atomic particles which may allow for differences in timing effects.
So you would just have mass, time and radiation from time period to another, possible skipping through a fold/wave.
We already know that time is variable and not a constant, but we pass through it without being able to measure any difference where we are, only is comparison to another area. Because we are unable to measure time outside our environment what we consider a gravity wave may in fact be a time wave, gravity simply being a drag factor of mass. There is no reason to believe that the passage time is smooth and in fact it may cycle like a sine wave or be fragmented, speeding up and slowing down. This would also suggest that there could be no such thing as infinite gravity in something like a black hole, but that it would have the effect of an immovable drag that could not locally budge in time, only evaporate. The matter would still be in our own universe but would be more like a pin holding the mass in place, or a weight too heavy to push, like a boulder on earth. Only something more powerful or a similar item will make it move locally.
Is time travel possible by either artificially creating another dimension of time, or finding a parallel existing dimension which has a different flow, and side stepping back and forth?
Dodging the pedestrian.