A soft-boiled duck egg should cook for six to seven minutes, resulting in a slightly runny yolk. A hard-boiled duck egg should cook for nine minutes.
Duck eggs are larger than hen eggs, and duck eggshells are more delicate. Keeping the eggs at room temperature before cooking reduces the risk of cracking. Hard-boiled duck eggs form a gray line around the yolk if they are not consumed immediately after cooking. Chilling the eggs in a bowl of cold water before peeling is useful to prevent discoloration. Duck egg whites contain more protein than hen eggs, and the yolks contain more fat.