It depends on the snails
Now I admit, I have some irritating snails. They've gotten massive, so everytime they crawl under anything that isn't glued down, it tumbles. They also latch onto my hermit crabs...of course trapping the poor hermits. I think the snails get a bit bored. For some reason, they also meet up on the front of the tank glass right about bedtime...but in the morning, they've moved. I have no idea lol
Some snails are nocturnal though, so it looks like they do nothing all the time...and you'll pick them up ten to fifteen times to see if they're alive before you realize what is up with them lol