With those sort of time frames, surely it would be much more easier to just catch a flight to Ho Chi Minh City. Then either stay on the main land in a comfortable hotel over night or, far more risky, find out when it is due to land in HCMC, add a few hours and book a later flight to PQ. Only downside is because it would probably be two tickets, any missed connection would be something for you to sort.
Great minds think alike rayza :-)
Haha! Pipped at the post! Expedia says cheaper for 16/10 but I checked on the airline site. Maybe some days are still less.