I was unsure about how well the moss would do in the bottle. I have not had to water it at all- it appears to be fairly self-contained even with the lid off. It also turns out that i have five small unexpected inhabitants inside the tiny landscape...five snails, each about 4 mm in size! They came in with the soil i suspect. There is also a mysterious plant sprouting inside, perhaps a grass of some sort. I swear it's better than watching tv...sometimes the snails try to climb up the side of the bottle then fall back down.
You can see one of the in the photo below looking down inside the bottle (bottom right corner, the white dot). The moss itself seems to be getting longer. It looks like tiny coniferous trees if you look close, the bottle is too steamy right now to see.
See the original post with directions here.