Precise cooking time: how to figure it out How do you figure out the exact time how long to cook something?

Do you use binary search?
It is very simple.


Note the time you start cooking it, and the flame/power setting/temperature. 
Check periodically to see if food is cooked
When food is done: record time and subtract from start time. 


If you cook the same dish a few times, you can average it out.  A lot of cook times are approximate anyway; you have to check the dish a bit before it should be done to make sure it hasn't cooked faster than expected.