Using a timer to track cooking time is the best way to ensure that hard-boiled eggs are done. Hard-boil eggs can be cooked using multiple techniques, but all techniques lead to a cooking time of about 10 to 12 minutes in a pot of boiling water.
Eggs can be added to boiling water, or they can be added to cold water and brought to boil. Either way, a timer should be set from the point at which the eggs are in actively boiling water. Once the timer ends, the eggs can be removed from the water and cooled until they can be handled for peeling.