The sunset seat
Pick a flight. This works out where the sun sits, minute by minute, and which window gets it.
Seattle
Los Angeles
Sit on the right.
Sunset about 1 hr 05 in.
Look from about 4:37 to 5:29 PM, LAX time.
and you would see it.
1 hr 05 in
Sun on the horizon, 82° right of the nose
5:03 PM
An estimate along the great circle at 470 knots and 35,000 ft, counted from takeoff. Real routes, winds and runways vary.
The month by month version is in the field notes.
Skycap says this for your own flight. See what it does.