How many hours before I land in Vietnam must I complete the arrival declaration?

You can file the Vietnam arrival declaration within 72 hours before you arrive. The portal lets you choose an arrival date from today up to the next two days, so you cannot complete it weeks in advance.

A practical plan is to file the form once you have booked your hotel and know your flight number, ideally the day before you fly. If your flight is delayed past your chosen date, check the form on the portal and submit a corrected one, because the date is part of the data immigration sees.

Keep the QR code on your phone and a printed copy if you can. You file it at prearrival.immigration.gov.vn, and it is free.

Your visa has its own timing. If you are cutting it close, look at the urgent e-visa options, because the visa must be approved before the arrival card can be completed.