Your eVisa is valid for 30 days from the arrival date included in your application. As long as you can enter Vietnam between the "valid from" and "until" dates stated on your eVisa document, you’ll be able to visit.
If your eVisa is expired, however, and you’d like to enter Vietnam after the expiry date, or if your travel date is now earlier than the arrival date on your application, you’ll need to apply for another eVisa. Feel free to reach out to us, and we’ll help you figure out your next steps.