AC 854 then BA 1390 at Heathrow
Toronto → London → Belfast City
Timetable, London time
06:30AC 854 from Toronto at the gate
06:15BA 1390 to Belfast City leaves the gate
23 h 45 apart on the timetable, overnight
BA 1390 leaves 23 h 45 after AC 854 arrives on the timetable: more than half a day, so not a connection we count.