AA 1509 then DL 903 at Atlanta
Cleveland → Atlanta → Seattle
Timetable, Atlanta time
09:08AA 1509 from Cleveland at the gate
21:15DL 903 to Seattle leaves the gate
12 h 07 apart on the timetable
DL 903 leaves 12 h 07 after AA 1509 arrives on the timetable: more than half a day, so not a connection we count.