AS has gone back to a heavily banked structure in both SEA and PDX so the flights from the outstations are timed to feed those banks. SEA's first bank is in the 8:00 hour so most of the first arrivals from outstations are timed to arrive about an hour before (thus a 6am or so flight from GEG). Meanwhile PDX's first bank is in the 7:00 hour so the outstation flights to PDX leave earlier (just after 5am for GEG).