Do my arrival and departure dates have to be exact, or can I travel anywhere inside the visa period?

Your dates do not have to match your flights exactly. You may enter on the start date or any day after it, and stay until the end date. Entering earlier than the start date is the one thing you cannot do.

Adding a buffer is a sensible choice. Applying from 20 December to 28 December covers a delayed or rescheduled flight. The cost is the same for a single-entry e-visa of 1 month or 3 months, so a longer window costs nothing extra.

The only limit is that you must leave by the end date. If you plan to stay a few extra days, choose the end date with room.

Keep the same entry gate in mind, because it is listed on the visa. Read more about the rules on evisa.gov.vn, and our e-visa guide explains validity. You can apply for your Vietnam e-visa online.