I use "ticks" to represent time here since you can speed the gameplay artifically.
Disussions in realtime minutes is moot.
I assume everyone understands what constitutes a colonists' performance and what affects that like, morale, happiness, comfort, services, disasters, their traits, their flaws, etc.

1 Sol = 750,000 ticks, 3 workshifts @ 250,000 ticks per shift.

Each "Teaching Building" is based on evaluation time except Grade Schools.
A University evaluation time is 300 points. (Think college credits)
A Sanatorium evalution time is 200 points.
A Grade School has no evalution time, instead a Child stays in school until they are a Youth (Age 6).

A colonist earns training points toward their evalution in the University and Sanatorium.
The faster they earn those points the faster they graduate.
A Child earns training points while in school, the amount of points will dictate which traits they gain in life.
There is no benefit to graduating a child early. As a matter of fact, its a detriment since they will have less points.

Colonists earn credit for time spent in class known as Gain Points. (think of this as attendance roster)
Colonists earn eval points (think college credits) based on their performance plus the time (Gain Points) they spend in a school.
If they are not in school (ie: they are out of their shift and at home idle or elswhere) then they do not earn points.
A low performing colonist will take longer to graduate.
Closed shifts in schools will cause colonists to take longer to graduate as colonists will compete for the shift.
For the nerds:
gain points = gain_points + MulDivRound(unit.performance, gain_point, 100)
eval points = MulDivRound(gain_point, time, g_Consts.WorkingHours * const.HourDuration)

Below are some observed statistics for a colonist to graduate:

University Optimal Scenario:
Default Time for Graduation = 300 eval points needed.
Assume colonist at 200% performance.
University normally gives 20 gain points per 30,000 ticks while colonist is in their shift.
Evaluation Breakdown as follows:
One entire shift = 250,000 ticks, thats 8 times a colonist can earn points if they stay for the entire shift.
I call 30,000 ticks a trainingslot.
If they stay for 1 training slot of the shift that is 60 gain points.
Gain Points = 20+((200*20)/100) = 60
Eval Points = ((60 * 30000)/(8*30000)) = 7.5
The Eval Points (college credit) formula (see above) evaluates to 7.5.
Maximum eval points per shift/sol this colonist earns = 60. (if they stay)
At this rate (300 eval points needed) they graduate in 5 sols.
With Martian Adaptation and 200% performance its 40 gain points per trainingslot which when all is calculated results in graduating in 2.5 Sols.
Math makes my head hurt.

Real observation for a typical game in a University:
Most colonists are not near 200% performance (some are and some get more, trait dependant), and some colonists idle around and dont go to their shifts in school or dont go for the full 250,000 ticks.
In a test colony I use that has 750 colonists:
Observed average eval points earned for Martian Born with Adaptability Tech is 14 per training slot.
Observed average Non Martian Born = 5

So in practice, a Martian Born colonist with average performance that never misses their shift will take 3 Sols.
However they never stay for the entire shift resulting in between 5-8 Sols.
A non martian average performance colonist that never misses their shift will take 7.5 Sols.
However they never stay for the entire shift resulting in between 7.5 - 15 Sols.
Some go faster, some go slower. Performance of the colonists vary widely and so do their visitation habits.
Get a colonist thats a hypochondriac and they may miss part of their University shift sitting in the infirmary.

Sanatoriums Need 200 eval points to graduate. You can do the math.

Grade School - Completely based on Age, so it takes time.

Use this mod to speed up earning these points.