BA 294 then BA 870 at Heathrow
Chicago → London → Budapest
Timetable, London time
06:55BA 294 from Chicago at the gate
19:25BA 870 to Budapest leaves the gate
12 h 30 apart on the timetable
BA 870 leaves 12 h 30 after BA 294 arrives on the timetable: more than half a day, so not a connection we count.