I give a snail about a week to move before throwing it out in my ponds. You can put the snail in a bucket of water and set it aside with some food and see if it moves over a few more days. Taking the snail out and smelling it will help to decide. If the snail is in a different place each day but you never see it out moving, it is coming out at night. Surprise it after the it is dark with a flashlight or room lights to see what it is doing.
Some snails only come out at night.
Effects of Water Hardness on Snails' Shells Snails require the calcium, magnesium, and other minerals to grow and maintain their shells. If you see snails with holes in their shells, the water's hardness is too low. Aquarium stores sell chemicals to increase the water's hardness. Ramshorn snails are said to be most effected by too soft water while Malaysian trumpet snails usually fare better. Prevention of Adding Snails with Live Plants By soaking live plants before adding them to a tank, fewer snails will end up in the tank or pond.