It's ok to add fish after the cycle has finished, but I've always been told, I never seem to follow my own advice, but that's just me, LOL, it has cost me in the past, a LOT, but anyway, waiting to add the corals is suggested because it gives the tank a chance to fully cycle and get good growth going on not just the bacteria, but also on the little critters that we can't really see that keep everything else in the tank, including the corals, nice and healthy. Also gives the tank a chance to fully stabilize. Just softies shouldn't be too much of a problem, but I highly recommend waiting at least 6 months before adding any kind of SPS, chalices, or clams.