DL 9951 then UA 521 at Atlanta
Queretaro → Atlanta → Houston
Timetable, Atlanta time
20:38DL 9951 from Queretaro at the gate
15:57UA 521 to Houston leaves the gate
19 h 19 apart on the timetable, overnight
UA 521 leaves 19 h 19 after DL 9951 arrives on the timetable: more than half a day, so not a connection we count.