By fishless,do u mean just no fish or nothing in the tank at all? Specifically live rock. BC if u have good lr then your ammonia should spike relatively fast. Now by good I mean lots of life. Worms,clams,alage, ECT. I have a lfs that carries great rock. BC of that my tank ran fishless for a month but I did 2 water changes. During that time I saw the worms and amphipods in the tank fairly regularly. I put 3 fish in and haven't had an issue. I do add fish slowly tho prob a month between additions. So basically if u have good lr your h2o changes shouldn't hurt much