BA 349 then IB 726 at Heathrow
Nice → London → Madrid
Timetable, London time
21:05BA 349 from Nice at the gate
19:40IB 726 to Madrid leaves the gate
22 h 35 apart on the timetable, overnight
IB 726 leaves 22 h 35 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.