I did a bit of searching, but wasn't able to find anything concrete. Hope someone can answer this quickly before we make a big mistake.
http://wiki.ffxiclopedia.org/wiki/Category:Salvage
http://wiki.ffxiclopedia.org/wiki/Remnants_PermitReentering: You may obtain another Remnants Permit after midnight JST. This is based on the day that the Remnants Permit was purchased, not the day that the character entered Remnants, so it is possible to enter Remnants twice in one day if the character has a pass that was purchased the day before.
I know you can do two events back-to-back, but what about if you want to do one event one day and another the next (at a much earlier time)?24 hours (Earth time) must pass after purchasing a Remnants Permit before you are able to purchase a new one, and you may only hold one permit at a time. However, unlike Dynamis and Limbus, it is still possible to participate in two successive Salvage runs: buy a permit, wait 24 hours, use the permit on a Salvage run, then buy a new permit and you will be able to enter Salvage again immediately.
Also, I looked on the BGWiki but didn't see much, would be useful to have once someone who's in the know replies.
Thanks in advance!
XI Wiki

