After introducing them to the tank, they started moving right away. All three of them went up to the waterline and stopped. For the first two, I moved them down, afraid they would escape, but they never moved again. I exchanged the first and second one, placing the second in the tank and putting the first in the bag the second came in. The first never moved again and I tossed it out with the bag after a day. The second is still on the bridge and hasn't moved since Tuesday. For the third one, it also climbed to the waterline, but this time I didn't touch it. Now it's in the corner as though it fell from it's spot. They don't smell, but I'm not hopeful. I will give them a chance and keep them around for a few days.
I do not have an airstone. I assumed the hang-on-back filter was enough. Let me know if that's a bad assumption.
I set up the tank two weeks ago, I thought that would be enough for the nitrogen cycle. Though, I started this snail journey about a week after setup.