Hello Moses,
This is a fairly slow growing moss, but the growth speed of any moss is dependant on the environmental variables, eg. lighting, nutrients, moisture, etc.
This moss grows in a very tight mat entangling it's fern like leaves together, I don't know that you would ever have to cut it and if you did it would be a long time from the original setup time.
I am not on here much since I first posted this since I have had such a large response from ebay and other sites, my moss and exotic plant sales hav e kept me way to busy.
Feel free to email me if you are interested in trying some of this or my other mosses and plants.
Have a great weekend.
Nat.
wildcrafter1969@yahoo.com
http://stores.ebay.com/Organic-Earth-Art-and-Rare-Finds