Stir well. When it comes to the boil, turn the heat to low and let simmer for at least 30 minutes, maximum 45.
The cooking time is not fixed, it depends on the quality and type of tomatoes. Usually, you taste it and you can tell when it's ready.
If you can't tell by the taste, use time to guide you and the texture - it should be slightly denser. Usually, the sauce made from fresh tomatoes takes longer to cook.
The boiling process here is very important. This way the tomatoes will have less acidity and become sweeter.