You could show up for AC146 (00:35) and they'll put you on the list for standby in J. Extremely high chance that you'll get that cleared unless there's been some sort of IRROPS cluster**** in the days before. Otherwise, you could wait for AC164 (11:15).
J AP rewards have free standby for any flight that day.
Day before requires a ticket change with space available in AP J redemption inventory.