Age of the egg, the temperature of the water when putting it in, the type of egg being used, and the size of the egg all impact cooking. It’s best to use fresh, new eggs and room temperature, large eggs when following these directions.  This will help you to achieve the perfectly cooked hard-boiled egg. I've found Ninja Foodi hard-boiled eggs to be the most reliable method. While no process is perfect, this one has definitely produced the most consistent results for me.