I would like to encourage you to use a Fissidens rather than any Grimmiaceous species. I think Grimmia and its related genera tend to be species found in drier areas and may prove more difficult to grow in your time frame.
On the other hand a Fissidens species loves humidity and wetness and grows rather vigourously and I believe that it can handle your substrates especially if watered or rather missted 2 to 3 times daily. Fissidens will also colonize onto bark or cork under such humid conditions.