As ammonia hits zero, nitrite will be climbing. Then as it drops nitrate will be climbing. Only when ammonia and nitrite are ZERO is it time to think about livestock... and I'd personally give it an extra week to be safe.
I don't mean to sound preachy, but the first thing ANYBODY should do when looking into setting up a SW tank is learn about the nitrification cycle. It's the most basic thing that keeps animals alive, and the very first thing you have to "do" when starting.