Early pulling S ranks isn't against the rules but it doesn't allow enough time for most people to travel to them in time. It is frustrating to drop what I'm doing to head to the spawns only to miss out on them time and time again.
An easy fix for this that hurts nobody and only benefits the community is to put a 5 minute immunity timer whenever an S rank spawns. It will allow plenty of time for people to world hop and travel there.