Plenty of people just let their eggs cook to oblivion to ensure the yolk is hard. But 10 minutes is really all you need for a light-textured white and a fully cooked yolk. If you want a soft-cooked egg (hard white, soft yolk), subtract 4 minutes from that. Take it longer than that and you may end up with an unpleasant (but harmless) sulfur smell. And just because they’re out of the hot water doesn’t mean they’re done cooking. Eggs can overcook if you don’t cool them down properly in ice-cold water when the cooking time is up.