2. Steaming hairy crabs generally takes about 15-20 minutes. But the steaming time of hairy crabs is related to the size of hairy crabs. For example, crabs with a weight less than 3 should be cooked and steamed for 10 minute, crabs with a weight of 4 should be cooked and steamed for 12 minute, and crabs with a weight greater than 4 need about 15 minute. Generally, it takes two minutes to extend the time every one or two minutes. If you are not sure whether the hairy crabs are steamed, you can break the back cover of the hairy crabs. If you see the crab meat solidified in the lid, it means it has been steamed and cooked thoroughly.