Step 3: Boil tomatoes
This time will vary according to the size of your tomatoes (smaller tomatoes will cook faster!), the size of your pot (larger quantities of water have greater thermal mass!), and the number of tomatoes you drop in each time (more thermal mass of tomatoes drops the water temperature!).
The goal is to boil the tomatoes just long enough to cook the outer millimeter or so of tomato skin and connective tissue so the skin will detach easily, while leaving most of the tomato in a nearly-raw state. Do some test runs, and adjust your timing as needed. If you see the tomato skins starting to split down from your original cut, they're definitely done - yank them out immediately, and consider dropping the time for your next batch.