Not necessarily, however, the arrival date you mention in the application has to be the earliest date you plan on arriving in Vietnam but there is no restriction that you must arrive on that date – you can arrive at a later date too. However you must leave the country before the departure date.
For example: If you have applied for one month visa and set the arrival date to be Oct 1, 2020, your approval letter will be valid from Oct 1, 2020 to Nov 1, 2020. You can enter Vietnam any time between the validity periods but have to leave before Nov 1, 2013.
