I've been to Saigon numerous times, It is better not to come there before 3-4 PM. I believe they are open pretty late (like 3 am). And the place is busy. So if you show up before 3 PM next day the best you can get a really tired girl who just wants to sleep.
The best times to go there actually between 5 - 8. Then you get a good selection and girls are not tired.
And sorry, forgot to add, I highly recommend this place. They have the most variety (from places i've been to).