While fresh snails bought in markets no longer need to be purged before using, they do need to be cleaned and then boiled before being prepared in a sauce or added to a rice dish. It is important that the snails are brought slowly to a boil. The snail will emerge from the shell and then not quite be able to retract back inside, making the meat easier to extract and eat. A snail dropped into boiling water will quickly retract and be much harder work to eat.
Scrub the snails clean of slime and grit using plenty of water, a bit of wine vinegar, and salt. Rinse very well with running water.
Put the snails in a large pot and cover with water. Over low heat, slowly bring the water to a boil, allowing at least 30 minutes. When the water breaks a boil, remove the pot from the heat, and dump the snails in a large colander to drain. Rinse the snails with running water and clean the pot. Return the snails to the pot, cover with fresh water, and bring to a boil over high heat. Add the garlic, bay leaves, and thyme; reduce the heat to medium-low; and gently boil uncovered for 30 to 60 minutes, depending on how the snails will be cooked. (If they will be stewed or braised, 30 minutes is enough; if they will be used in rice dishes, boil for 60 minutes.) They are now ready to use according to the recipe instructions.