15-20 minutes. Crabs usually need to be cooked for 15 to 20 minutes, 3 to 4 taels of crabs, need to be cooked for 15 minutes, more than 4 taels of crabs need to be cooked for 20 minutes, cooking crabs can not be less than 15 minutes, otherwise it can not play the role of sterilization and disinfection, the time should not be more than 30 minutes, otherwise it will affect the freshness of the crabs and the edible taste. So the crab is cooked in about 15-20 minutes.