I went through that process not too long ago when I set up my SW tank... With my first (biggest) batch of rock, the ammonia and nitrites were through the roof, and I had to do daily water changes. I did between 5-10 gallon changes, and my tank is technically rated as a "60" gallon (although with sand, rocks, and everything in there it only holds about 40 gallons of water).
My best advice to you is to test water parameters daily and do as much changing as necessary to keep the ammonia and nitrite levels at or below 1.0 ppm and your nitrates 5.0 ppm to preserve as much life on the rocks as possible.
You'll have to do this until the rock begins to be able to do it on its own as the bacteria levels recuperate and regrow, which could take anywhere from a couple days to a couple weeks depending on how the rock was shipped, air exposure time, etc.
Hope that helps, and have fun watching all the cool life-forms begin to emerge from your rock as the cycle winds down!
