I was on UA 890 this past Saturday and we landed early in LAX around 8:10am, and of course sat until Customs opened at 8:30am. I think the hours have to do with what UA pays for the facility.

Part of the problem is they are closing the flights in Narita 15 minutes early for security reasons, and then end up pushing back early.

Was one of the best flights I have had on UA...trip report forthcoming.