Inverts, such as snails or crab should be quarantined the standard 76 days unless you increase temp to 80.6, then it’s a 6 week qt. So depending on your DT stocking timeline, you might be able to put them in now.
If your rock was from the ocean or another reefers tank, it’ll need the sand QT time.
Check out humble fish’s forum. Lots of this info is outlined there