BA 581 then UA 949 at Heathrow
Milan → London → San Francisco
Timetable, London time
14:35BA 581 from Milan at the gate
13:45UA 949 to San Francisco leaves the gate
23 h 10 apart on the timetable, overnight
UA 949 leaves 23 h 10 after BA 581 arrives on the timetable: more than half a day, so not a connection we count.