You should slow yourself down. Doing the first water change will not hurt or cost too much, so go ahead and so it. But keep a good eye, magnifying glass is good for this, on the rock look for signs of life, sponges, feather dusters, worms, pods, coral etc. If you can see some life worth saving then do the water changes. In my small mind a soft cycle would be done by someone that has purchased uncured rock with an abundance of life on it. I am, I feel like I am repeating myself here, not convinced that your rock is anything more than mostly base rock that does not contain much if any life more than the coralline you can see. But I am not there, I cannot see what you can see.
