This trip changes pace twice: busy city streets give way to Da Lat’s cooler hills, then to the Nha Trang coast. You have two full days in each place. That is enough for a historical visit and another neighbourhood in Saigon, a coffee day and an architectural outing in Da Lat, and a temple day followed by a water or bathing activity.
The hotel allocation is three nights in Ho Chi Minh City, three in Da Lat and three on the Nha Trang coast. Days four and seven are the moves, so their afternoon plans stay short. Book the domestic flight before settling the highland hotel dates, and choose a morning road departure for the coastal move. A shared van brings the cost down; a private car lets your party agree its own breaks and final resort address.
February or March is a useful weather compromise. Saigon is outside its main May–November rainy period, Da Lat’s wetter April–November months have not begun, and Nha Trang’s September–December rainy season is over. Pack a layer for the hills alongside beach clothes. Later in the year, keep the café and architectural visits flexible around rain, and let the boat operator decide whether conditions permit the water outing.