UA 901 then BA 870 at Heathrow
San Francisco → London → Budapest
Timetable, London time
07:25UA 901 from San Francisco at the gate
19:45BA 870 to Budapest leaves the gate
12 h 20 apart on the timetable
BA 870 leaves 12 h 20 after UA 901 arrives on the timetable: more than half a day, so not a connection we count.