dropping snails into a tank that has virtually the same parameters as LFS won't matter. A slight diff in pH, alk etc wont do them harm. But that case is rare, and as a rule of thumb, nothing should ever be put into a new environment without proper acclimation.
Snails I acclimate for around 1 hour or so, doing 1/4 cup every 10-15 min. or so into LFS bag.