I would also allow more than 1 hour between flights. You're really dependent on your long San Diego to Tokyo flight being on time.
If plane is delayed, you might make your connecting flight, but your checked bags might not. Will you be staying in one place in Ho Chi Minh city long enough for JAL to get your bags to you? I'm assuming on international flight you'd have checked bags.
I'm reminded of DH & my own experience and those of 2 canadian ladies last year flying to Italy. We flew Vancouver to Toronto to Rome on Air Canada with an 1.5 hour layover time. Our Toronto flight was delayed 45 minutes from landing. We raced to the Rome plane but our bags did not. We didn't know until after almost a whole day in Rome if we'd get our bags back.
We met the 2 ladies at a lost baggage claims desk in Rome airport. This lost baggage desk was run by a contracted Italian company. The ladies flew a similar route the day before us, except from Ottawa to Toronto, for a cruise leaving outside Rome. They had arrived 2 days before cruise, and the italian contractor & Air Canada still had no idea where their bags were. So they were resigning themselves to finding some new clothes in Rome and boarding ship with far less than planned.
JAL, I'm sure, is much more efficient than some italian companies in getting missing bags to their customers. But your end destination of Ho Chi Minh city does make me wonder...