That does require peeling apart the layers of what seems to actually be happening, as opposed to the mathematical modeling.

As I learned the simple version, back in the 70's, you have to subtract the motion of the frame from activity occurring within it, because the combination still can't exceed C. At the point the frame itself is moving at C, there is no activity possible within it, so no time or distances can be measured.

As for gravity, that's an entirely more speculative issue, as it is apparent no one really understands gravity, given the conflicts in the field between the Dark Matter proponents and the ones in favor of MOND.

My thought on the subject is that we are looking at it backwards. Rather than gravity as a property of mass, mass is an intermediate, stable, somewhat dense stage of a centripetal dynamic that goes from the barest bending of the light, to the vortices at the center of galaxies.

What causes it? It seems to me the most elementary factor is that when waves synchronize, the effect is centripetal. One big wave is more efficient than lots of little ones. Lasers are synchronized light waves and they are certainly compacted energy. Consider the quasars shooting out the poles of galaxies are essentially giant lasers.

So quite literally, things fall together, as an entropic effect. No gravitons required. No Dark Matter necessary.

So next part of the question, how does this slow the measure of time? Actually I hadn't ever asked myself that. Good question.

So lets step back and consider that while gravity/synchronization pulls wave patterns together, the underlaying energy naturally goes the other way, radiating out. Galaxies are energy radiating out, as structure coalesces in.

The consequence is harmonization, as all the energy gets traded around and settles toward equilibrium. So between black holes and black body radiation.

The one idea is tighter feedback loops speed up processes, which certainly applies to biology, aka, metabolism, so it likely extends down into he subatomic realm.

Here is an interesting interview, from many years ago that I saved, because it re-enforced my sense that waves are more fundamental than particles;

http://worrydream.com/refs/Mead%20-%20American%20Spectator%20Interview.html

To the extent waves either synchronize, or harmonize, we have organisms and ecosystems, so why not particles and fields?