AA 6504 then AA 5418 at DFW
Flagstaff → Dallas-Fort Worth → Harlingen
Timetable, Dallas-Fort Worth time
09:28AA 6504 from Flagstaff at the gate
21:48AA 5418 to Harlingen leaves the gate
12 h 20 apart on the timetable
AA 5418 leaves 12 h 20 after AA 6504 arrives on the timetable: more than half a day, so not a connection we count.