Just test the water daily, when your ammonia and nitrite readings are ZERO, then it is done. Your nitrates will climb steadily, so expect the reading to rise daily until the cycle is done. Then add the rock to your tank. But only add it after your levels stay zero, except for nitrates of course. And during this cycling...it is a good time to keep a close eye on it for unwanted pests like mantis, aiptasia, etc...