UA 503 then BR 643 at O'Hare
Boston → Chicago → Anchorage
Timetable, Chicago time
12:46UA 503 from Boston at the gate
11:55BR 643 to Anchorage leaves the gate
23 h 09 apart on the timetable, overnight
BR 643 leaves 23 h 09 after UA 503 arrives on the timetable: more than half a day, so not a connection we count.