Can we calculate the fastest passage of time?

I recently watched one of the several "time causes gravity" videos on YouTube. It led me to a question. Simplifying the universe just a bit and assuming we can represent the passage of time as a "velocity" (V_T), then we know:

$$lim limits_{V_x,y,z to c} V_t = 0$$

Said another way, when an object’s velocity in space is equal to the speed of light, the "velocity of time" is equal to zero. My question, then, is this:

$$lim limits_{V_x,y,z to 0} V_t = ?$$

Said another way, what is the maximum "velocity" of time if an object becomes absolutely motionless in space?

The idea that there is such a maximum appears supported by the idea that clocks move faster the further they are away from Earth’s gravity well. If I’m oversimplifying all this properly, the idea is that the force of gravity represents a "velocity" such that the further away one gets from a gravity well, the lower the overall velocity of the object, and the faster time passes. (And this is complicated by the rotation and orbit of the Earth, the orbit of the solar system, the motion of the galaxy, etc.).

Nevertheless, is it possible to calculate the fastest possible passage of time?

NOTE:

I understand that the passage of time most likely must be expressed in our reference frame. A human on a theoretical space ship traveling up to the speed of light and back again (and ignoring a whole lotta stuff) would perceive the passage of time as "normal" even though it’s not passing at $V_x,y,z = c$. So, I expect an answer to my question having to be expressed in the context of Earth’s reference frame — but I could be wrong.