UA 558 then DL 5679 at Boston
Denver → Boston → Louisville
Timetable, Boston time
13:42UA 558 from Denver at the gate
09:55DL 5679 to Louisville leaves the gate
20 h 13 apart on the timetable, overnight
DL 5679 leaves 20 h 13 after UA 558 arrives on the timetable: more than half a day, so not a connection we count.