Not Scientific or a Strict Pattern

I'm not obsessing about belts, etc.  I'm very committed to the journey, etc.   I gladly accept the fact that it takes 10 plus years to get a black belt. Still, I'm curious about a quantitative approach to jiu jitsu rank progression.

10 years of training once a week is not the same as 10 years of daily training, etc.  Something that motivates me is calculating the next step in the path.  There are 20 steps to one's black belt (beginning at white and getting four stripes on it plus blue, purple, and brown).  I'm not sure how much will be required for stripes and belts.  Perhaps an average of 75 classes will be required between each step. (In most cases, stripes on white and blue belts come more quickly.)  This sets the bar at 1,500 hours (which is not scientific or a strict pattern).  

If one trains 3 hours a week (which boils down to a single class every other day), he will get about 150 classes per year (allowing for gym closures, vacations, sickness, etc.).  With 10 years of consistent training, one might be able to get his BJJ black belt.