UA 26 then WN 988 at Denver
London → Denver → Buffalo
Timetable, Denver time
14:25UA 26 from London at the gate
11:50WN 988 to Buffalo leaves the gate
21 h 25 apart on the timetable, overnight
WN 988 leaves 21 h 25 after UA 26 arrives on the timetable: more than half a day, so not a connection we count.