They tend to be on the delicate side, but not overly so. I'd wait until your cycle is definitely on the "down" swing - you want ammonia & nitrites to be at zero, and nitrates coming down (and preferably less than 50ppm) before you add snails/hermits.
They should be acclimated slowly, as they are sensitive to rapid changes in salinity/temp & pH. Once properly acclimated, they are easy to keep, as long as your water parameters remain stable, salinity is not too low (1.024 or higher), and they have sufficient food.
Oh yeah - and supply extra shells for the hermits, so they don't kill the snails for their shells.