What time does the post office open on island on saturday?
Which post office do you want to know about, and which definition of "open" are you using? There are:
Bulk Mail Acceptance Hours
Last Collection Hours
PO Box Access Hours
Carrier Facility Hours
Here is info for some of the STX PO's: https://tools.usps.com/go/POLocatorAction!input.action?address=00850&radius=20&locationTypeQ=all&tAddress=&tAddress1Ams=&tAddress2Ams=&tCityAms=&tStateAms=&tZipAms=&tCarrierRouteAms=&sWithin=20&sServices=&hoursSelected=%5B%5D&collectionBoxSelected=%5B%5D&collectionHoursSelected=%5B%5D&servicesSelectedBusinessOffice=%5B%5D&servicesSelectedOffice1=%5B%5D&servicesSelectedPassportOffice=%5B%5D&servicesSelectedOffice2=%5B%5D&approvedProvidersSelected=%5B%5D&allLocationsSelected1=%5B%5D&allLocationsSelected2=%5B%5D
Click the PO that you want for specifics. Or better yet, call the PO to confirm their hours.