BA 563 then BA 480 at Heathrow
Rome → London → Barcelona
Timetable, London time
10:30BA 563 from Rome at the gate
10:25BA 480 to Barcelona leaves the gate
23 h 55 apart on the timetable, overnight
BA 480 leaves 23 h 55 after BA 563 arrives on the timetable: more than half a day, so not a connection we count.