your live rock and sand are your fiolters they are encrusted with your anerobic or nitrifying bacteria if its good rock and sand it might not ake long at all thts why i always get "cured" live rock. once your ammonia and nitrite are reading zero it is then safe to add fish and corals but there are specific guidlines as far as lighting requirements and feeding for corals make sure u understand and can meet all the needs of your corals before purchasing and running the protien skimmer during the cycling period will also speed up the process by removing extra organics from the water that would turn into ammonia and nitrite.