There are a lot of factors.
First, the triggers (everything needs to be true for the event to fire).
- The province must be core.
- The province revolt risk must be less than 1.
- The province religion must be the national religion.
Plus, the province needs to be either the capital or bordered by a province owned by you and that has your religion and culture.
The MTTH is of 2400 months, and is changed by these factors:
- If your culture group is byzantine or turko-semitic, and the province has a greek or turko-semitic culture, there is a factor 0.05.
- If your national culture is baltic, west slavic or east slavic and the province culture is khazak, kirghiz, siberian or tartar, there is a factor 0.05.
- If your national culture is prussian and the province culture is saxon or pommeranian, there is a factor 0.05.
- If your country is european, and the province culture is european, and the province is not in europe, asia or north africa, there is a factor 0.05.
- If the province culture is from your culture group, there is a factor 0.8.
- If it's your capital, there is a factor 0.8.
- If you have the church attendance duty idea, there is a factor 0.9.
- If you have the divine supremacy idea, there is a factor 0.9.
- If your serfdom-free subjects slider is less than -1, there is a factor 0.9.
- If your stability is 1 or more, there is a 0.9 factor.
- If your stability is 3, there is a factor 0.9.
- If your stability is of 0 or less, there is a factor 2.0.
- If your stability is less than -1, there is a factor 2.0.
- If you have the idea humanist tolerance, there is a factor 2.0.
- If your slider serfdom-free subjects is of at least 2, there is factor 1.1.
- If the city is not your capital and has more than 10k of population, there is a factor 1.1.
- If it's more than 25000, there is a factor 1.1.
- If it's more than 50k, there is a factor 1.5.
- If it is more than 100k, there is a factor 2.0.
The factors are cumulative, so if your stability is of -3, your MTTH will be multiplied by 4.