The recommended cooking time for eggs to be fully cooked is approximately 6 to 8 minutes for hard-boiled eggs. This duration ensures that the egg whites are firm and the yolks are set, but still soft. The cooking time can vary slightly depending on the size of the eggs and the desired level of doneness for the yolks.

The reason for this range is based on the heat required to cook the egg whites and yolks to the desired consistency. Hard-boiled eggs require a consistent and moderate heat to cook evenly. At the lower end of the range, 6 minutes, the eggs will have a slightly runny yolk, which is preferred by some people. As the cooking time increases to 8 minutes, the yolks become more solid and less runny, appealing to those who prefer a firmer yolk.

According to the United States Department of Agriculture (USDA), eggs should be cooked to an internal temperature of 160°F (71°C) to ensure they are safe to eat. Boiling eggs for 6 to 8 minutes typically reaches this temperature, ensuring that any potential bacteria, such as Salmonella, are killed. It's important to note that the cooking time can vary based on the stove's heat and the size of the eggs. Larger eggs may take a bit longer to cook compared to smaller ones.

Additionally, the cooking time can be influenced by the starting temperature of the water. If the eggs are added to cold water, the cooking time may need to be extended by a few minutes to ensure they reach the desired internal temperature. This is because the eggs need to heat up along with the water before the cooking process can begin effectively.

In summary, boiling eggs for 6 to 8 minutes is the ideal cooking time to achieve a fully cooked, hard-boiled egg with a soft to firm yolk. This duration ensures safety and the desired texture, based on the guidelines provided by the USDA.