Like marshman said end of feb. but they will be very expensive. I also like Louisiana crab boil. It depends on how y'all want them. Spicy or not. Spicy use Louisiana and get the big bag. One small bottle of zatarans liquid crab boil. I find that the Louisiana liquid is bitter tasting. I put potatoes in water first let them boil for a little (10 min or so) then I add the crawfish and any other seasoning I want ( sausage,onions,lemons,garlic,etc. ) I cover the pot and wait until I see steam coming out. Then I time for 5 min. Shut off burner add corn on cob if desired and let sit for another 10 min then I cool the pot with a garden hose by spraying the outside. Then from there taste and soak until they are as spicy as you like them! Dump them on a table and enjoy. Don't put them in an icechest while they are still hot or they will continue to cook and end up being mushy from overcooking. Don't stir the. Raw fish when you are cooking either or you will end up breaking up all the potatoes. I like to use red potatoes and not the little ones. I like to use the big ones and I cut them in half. It gives the potato more flavor. Another good crab boil that isn't as spicy but very flavorable is swampfire. That's crawfish.
Shrimp is a little more finicky. Only boil the shrimp for one minute then either ice the water or take them out immediately and spread them on the table. If overcooked they will be hard to peel. A huge pain in the butt!! Add about a tbs. of veg oil to the water prior to boiling for every pound of shrimp. That helps the shell break away from the meat and makes it a lot more forgiving on the perfect cooking time.