Since snails can pass randomly even when they are fully healthy (just due to old age), how often do you do a snail check to ensure that they have moved (and are alive)?
I personally will try to just check on them once a week or bi-weekly (with every species, to make sure that they are getting enough food, not stuck somewhere since I've had that happen before), but won't truly go on a search by moving things around if I don't see them for a full month or so.