Cooking crab is a very complicated process, however, it is very little time consuming.
The cooking time for crabs vary according to the type and size of crab and also whether you want to have them overdone, underdone or cooked just right.
In all the cases the cooking time for crabs varies from 6 to 10 minutes, if you plan to boil live crabs. You would have to throw them in a pot of boiling water. Blue crabs take 6 minutes and Dungeness are ready in around 8 minutes.
Also, in most of the crabs, the shells turn red when the crabs are cooked so also lookout for this sign.