TBIT unpredictable as the winds
A family I know came in HKG-LAX (CX/Y) on the 1:xx pm arrival in late March but didn't get out until past 4 pm. They said it was all immigration and not baggage/customs.
The key is the distribution of arrival times on a particular day, which can be unpredictable. TBIT trans-Pacific arrivals are all long-haul from a variety of Asian cities (beyond Japan) and that means knowing the arrival schedules is still meaningless, since every flight can get affected by the jet stream differently.
Am I right to say that being in F/C doesn't help if you're the 5th B747/B777 to arrive TBIT in 15 minutes?