BA 1399 then BA 822 at Heathrow
Belfast City → London → Billund
Timetable, London time
16:25BA 1399 from Belfast City at the gate
16:05BA 822 to Billund leaves the gate
23 h 40 apart on the timetable, overnight
BA 822 leaves 23 h 40 after BA 1399 arrives on the timetable: more than half a day, so not a connection we count.