It depends on your definition of done. My suggestion is to standardize your method and then just determine how many minutes you like. I use already boiling water with a maxed out flame and a good amount of salt, and the husk and silk removed, and I find 90 seconds is about right. You may find you like 2 or even 4 minutes. Be sure and use a pot that is big enough that the water won't cool down too much when you add the corn.