Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Vietnam to Slovenia as you normally would.
Related info for your journey
Useful info, stats and facts about Vietnam to Slovenia flights.
This is defined as Ho Chi Minh City Airport (SGN) and Ljubljana Joze Pucnik Airport (LJU). Codes like Ljubljana Joze Pucnik Airport are often used to just call airports uniquely. Portoroz Airport (POW), Maribor Airport (MBX) are other airports near this flight route and their unique identifiers/IATA codes.