actually you touched on an interesting issue Dave...
Just like the space close to any dense body...(Donald Trump for instance...hahahhaahahaahaha..)
time moves faster..
this mechanism isn't just the domain of Black Holes..
take 2 atomic clocks...
put one static on the ground...
put another in a high altitude jet...
take the jet into the upper atmosphere...
fly it directly over the static clock..
and the clock in the jet is moving slower than the one on the ground.

Gravity dictates a lot...including the flow of time..
and mass dictates gravity...

To come back around to the initial issue...
not all galaxies are disk like...
nor are all moving circularly...
bad enough that here..."what goes around comes around"...so to speak...with changes along the way...

there are some galaxies that have been viewed...[shudder]
that appear from our distant view to be pendulum shaped..
and swing back and forth..
time there...[shudder]
would not be pleasant...
it would be the equivalent of a trap...a roach motel of this universe...
(not that our circular time flow isn't a trap either ...of course...but the above would be a nightmarish existence for sentient life)