We arrived in Saigon on Friday night with a couple of hours to spare before our domestic flight to Hanoi. All good. It was around 9 pm. One hour later, waiting, waiting. One of the attendants took pity on us and organized our cases and hurried up the staff otherwise we would have missed our flight. All our paperwork was in order as I had gone through a local Vietnamese travel agent and been very careful to dot the i s and cross the t s. I wouldn't recommend VOA to anyone. Go through the process at home, it makes for less stress. We were surrounded by many angry people. One couple we spoke to had missed their flight the previous night and had to get new flights. It may work like clockwork at certain times but I don't think it is worth the hassle.
I did post this as an answer on another post but wanted to put it out there as its own separate issue.