That seems to be the general consensus, 24-48 hours. I fought it twice in 2 days (1 per day) recently on my server, so yeah. However, it needs to be triggered by completing certain Fates, so if no one is working on it, it won't spawn. It doesn't just spawn on its own. If it hasn't spawned in the last few days on your server, I would try to spawn it yourself or get a group together.

https://ffxiv.consolegameswiki.com/w...ost_Formidable