BA 923 then BA 348 at Heathrow
Hannover → London → Nice
Timetable, London time
11:55BA 923 from Hannover at the gate
08:40BA 348 to Nice leaves the gate
20 h 45 apart on the timetable, overnight
BA 348 leaves 20 h 45 after BA 923 arrives on the timetable: more than half a day, so not a connection we count.