The ideal way to thaw fresh-frozen crab legs is in the fridge for 8 to 10 hours, which keeps them consistently cool enough to avoid bacteria accumulation.
If time is short, immersing them in cool water also works. Since crab quality declines the longer it's exposed to air, the goal is to minimize the time from freezer to cooking.
When thawing inside a refrigerator, at least that air is cold. The FDA specifies that seafood should be kept in refrigerated spaces of 40 degrees Fahrenheit or below.
To cook the legs frozen, make sure they are fully immersed in boiling water or in the steamer pot. Just note the potential for unevenly cooked crab meat.
Cooking times are similar for boiling frozen crab legs compared to thawed: Plan for about 6 to 8 minutes per pound. If grilling, place them away from direct flames.
You can also quick-thaw the legs under running water or immerse them in a bowl of cool water for half an hour. Just replace the water every few minutes so it stays cool.