The ideal cooking time for eggs in an egg cooker is typically around 6 to 7 minutes for a hard-boiled egg and 4 to 5 minutes for a soft-boiled egg. This duration ensures that the eggs are cooked to perfection without overcooking, which can lead to rubbery textures. The precise timing can vary slightly depending on the egg cooker's model and the size of the eggs.

The reason for these specific times lies in the science of cooking eggs. When eggs are boiled, the heat causes the proteins in the egg white to coagulate and the yolk to solidify. The cooking time is a balance between achieving a firm white and a runny yolk for soft-boiled eggs, or a fully solid white and yolk for hard-boiled eggs. According to the USDA, the recommended cooking time for hard-boiled eggs is 6 to 7 minutes, which is sufficient to cook the eggs through without overcooking them. For soft-boiled eggs, the cooking time is shorter, as the goal is to have a slightly runny yolk, which is achieved in 4 to 5 minutes. It's important to note that the size of the eggs can also affect the cooking time; larger eggs may take a bit longer to cook than smaller ones. Overcooking can lead to a tough texture and a greenish ring around the yolk, which is caused by the iron in the egg white reacting with the sulfur in the yolk. Therefore, adhering to the recommended cooking times ensures the best taste and texture.