B6 1397 then UA 1254 at Atlanta
Boston → Atlanta → Denver
Timetable, Atlanta time
15:32B6 1397 from Boston at the gate
11:14UA 1254 to Denver leaves the gate
19 h 42 apart on the timetable, overnight
UA 1254 leaves 19 h 42 after B6 1397 arrives on the timetable: more than half a day, so not a connection we count.