Q: When the best time to visit Saigon?
A: The wet season lasts from May to October in the south, and the best times for traveling to Saigon( Ho Chi Minh City) are late November through January.The biggest national festival in Vietnam occurs in late January or early February and is called Tet. This is an excellent time to vist the country, as the streets erupt with color and… well… festivities. Tet lasts about a week (or, for some Vietnamese party animals, up to a month) and is scheduled around the lunar calendar, so you’ll have to check for this year’s dates.
Source : Hochiminh City reviews, Trip advisor