<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by suranyi:
The post office at San Francisco Airport is open 24 hours, I believe.</font>
Having used it several times right before they closed, the SFO branch is open 6am-midnight.
BTW, if you ever want to know where the closest PO is with the latest pickup, just ask a patent paralegal or secretary...