BA 551 then BA 410 at Heathrow
Rome → London → Valencia
Timetable, London time
15:05BA 551 from Rome at the gate
15:00BA 410 to Valencia leaves the gate
23 h 55 apart on the timetable, overnight
BA 410 leaves 23 h 55 after BA 551 arrives on the timetable: more than half a day, so not a connection we count.