I read the post about a max number of FATEs per zone also. I've also seen 8 FATEs active simultaneously in Southern Thanalan. So unless the map is divided into smaller fate areas (ie: Broken Water, Zan'rak and the Sagolii Desert) it's likely that some some FATEs really are just on 2-2.5 hour respawns. I'm pretty sure this one, Giant Seps, and Enmity of my Enemy fall under those categories.