That depends on what kind of crab it is. If it is a foreign crab, you can wait until it has just died, but you should pay attention when cooking. It must be cooked thoroughly and it will take several minutes. Because the field crab died from the outside to the inside, it closed its eyes for an hour or two before it died. The field crab is just dead, but its brain is not dead, so there is no bacteria in it. So foreign crabs can be eaten as soon as they die. If it's a blue crab, you can't eat it. Because the blue crab died for an hour or two before closing its eyes. After the death of the blue crab, the brain has begun to rot and bacteria have proliferated. So the blue crab is dead and can't eat. But crabs caught in the sea, such as rock crabs, flower crabs and swimming crabs, are all dead and can be eaten. Because these crabs were alive when they were caught on the fishing boat, fishermen used tools to untie them from the fishing net as soon as they were caught. It took some time to untie them, and the crab died of lack of water and oxygen. At this time, the fishermen quickly refrigerated the crabs, so the crabs in the sea died after landing. So these crabs have no chance to reproduce bacteria after they die. So these crabs can be eaten after death.