First of all get rid of the damsels. You can cycle with a piece of shrimp just as easily. I don't see the reason in killing two fish when you don't need to. The ammonia from the cycle will likely burn their gills and stress them out hard at the very least. As far as the cycle goes, it will happen. How big depends on many things. Was the rock cured, in someone else's tank, or dry base rock? What kind of sand bed to you have and how deep? Pull the fish, add some raw shrimp or something, and continue testing for a few days.