Hi all, Too dry.
If the wood isn't fully saturated with water it will "suck" the water from the moss. This will keep on happening until the wood is fully saturated with water. You can try spraying it, but even then you may find you can't spray it regularly enough to keep the moss suitably damp.
Personally I would only attempt a moss dry start with wood that has been into soak for a long time, and then I would keep <"
the container sealed">. I would want everything beaded with water. It is likely that the rock isn't permeable, so any moisture will sit on top in a film or puddle.
The puddle will only evaporate when the relative humidity in the air falls below 100%. You still have to be a little bit careful, because warm air can hold a lot more moisture than cold air, and any rapid warming (of the dry start) is likely to lead in a fall in relative humidity and damage to the moss leaves (microphylls), even if there is a reservoir of water that can vapourise and return the relative humidity to 100%. You just have a lag period when relative humidity is lower than 100%.
You can get also get the reverse situation with a permeable substrate (a rock like tufa, or a really wet branch) where the rock etc acts as a water reservoir and a fall in the humidity of the air will lead to water vapour travelling out of the rock into the air (and the attached moss).
cheers Darrel