I just read, recently, that snails do need a long acclimation period. I'll quote from an article I found at ReefKeeping.com. This is an article written by Ronald L. Shimek Ph.D.
Here is a link to the entire article:
The Grazing Snails, Part I - Turbo, Trochus, Astraea, and Kin by Ronald L. Shimek, Ph.D. - Reefkeeping.com
Here is a summary of the text about acclimation:
Acclimation Problems, Or Why Do They Die? The complexity of internal anatomy in snails is one major reason why some of the Trochoideans seem to die easily, or otherwise not live through their full life spans in our tanks. Although most folks probably never give it a second thought, snails have a complex internal morphology. In many ways, the internal structures that the snails possess have allowed them to be very successful. It is not, however, a particularly "rugged" morphology when subjected to some specific stresses. Snail tissues often seem to be composed of thin layers of tissue that are very filmy and diaphanous. Consequently, they often suffer significant damage during water changes or during transport from a dealer's to an aquarist's tank. The circulatory system of snails may be very complex (Figure 5), and many of its vessels and channels can rupture under stresses caused by changes in salinity. The vessels in the kidney are numerous and delicate, and may rupture if the animal is not slowly acclimated when being moved from one set of water conditions to another. If the acclimation is too fast, the animal will die in a few minutes to a few weeks. If the snails are drip acclimated, the acclimation time may need to be on the order of five to ten hours for maximal survival.