UA 2123 then B6 1534 at San Francisco
Denver → San Francisco → Boston
Timetable, San Francisco time
23:09UA 2123 from Denver at the gatealso AC 3451, VA 8356, NZ 9072
22:10B6 1534 to Boston leaves the gatealso EY 8032
23 h 01 apart on the timetable, overnight
B6 1534 leaves 23 h 01 after UA 2123 arrives on the timetable: more than half a day, so not a connection we count.