The time it takes to steam a lobster tail depends on the weight of the lobster. A 2-ounce tail takes 10 minutes, a 4-ounce tail takes 12 minutes, a 6-ounce tail takes 15 minutes, an 8-ounce tail takes 20 minutes, and a 12-ounce tail takes 25 minutes. Anything heavier than 14 ounces generally takes more than 30 minutes to steam.
The best way to see if a lobster tail is finished steaming is if the meat is firm to the touch and white. One of the best ways to steam a lobster tail is to place a bamboo steaming tray over a pot of boiling water and observe it while it cooks.