OO 9909 then UA 4535 at O'Hare
Waterloo → Chicago → Pittsburgh
Timetable, Chicago time
16:47OO 9909 from Waterloo at the gate
12:48UA 4535 to Pittsburgh leaves the gate
20 h 01 apart on the timetable, overnight
UA 4535 leaves 20 h 01 after OO 9909 arrives on the timetable: more than half a day, so not a connection we count.