Let's talk about Hunts - a detailed rundown of their assumed mechanics

[BillyKaplan]

For Stormblood S ranks, 132 hours max respawn has been my personal observation, but it's not a forced spawn like an A rank. The spawn conditions still have to be met.

That's the same for all S ranks. That's why Nandi, for instance, will often spawn right by the aetheryte when its timer is up - it's set to go off, but you still need someone with a minion to run over its spawn point and those are the closest ones.