UA 3908 then AS 1421 at Houston
San Francisco → Houston → Portland (Oregon)
Timetable, Houston time
17:58UA 3908 from San Francisco at the gate
17:57AS 1421 to Portland (Oregon) leaves the gate
23 h 59 apart on the timetable, overnight
AS 1421 leaves 23 h 59 after UA 3908 arrives on the timetable: more than half a day, so not a connection we count.