Agree ... when we went there around 7+ pm last time in HCM
the waitress actually told us they are fully booked for the day.
You can wait awhile, if people leave earlier, then you can sit in their slot.
Waited for about 10min or so, one group left earlier.
Then the waitress told us, you only have about 25 minutes to dine in, before the next group comes in.
i always go at 2.30pm and theres a lot of seats at this time =)