If you schedule a trip to Vietnam, you should make the Vietnam visa application the first and prior to your scheme a few days in order not to miss your travel. You may highly pay the penalty fee from 20 US dollars to 50 US dollars to the official authority or more seriously you can be forbidden to enter Vietnam if you break them or enter Vietnam without appropriate application.
Swiss citizens are not in the visa exemption list so they are required to complete Vietnam visa application before travelling to be allowed to enter the country.