Usually, an EVUS update is valid for 2 consecutive years, or until your passport or Visa expires, whichever comes first. This means that as long as your EVUS is Successful for travel, you do not have to enroll again during the validity period.
You are only required to have a valid EVUS when arriving only. In case your EVUS expires after being admitted into the United States or during your stay, it will not affect your departure.
An EVUS application will not allow you to remain in the U.S. for 2 years. It only allows you to visit the US under the specified terms on your Visa. The Visa conditions would enable you to remain in the US approximately 6 months or less.
Your EVUS will be rendered invalid if:
In any of those cases, you will be required to apply again for EVUS. A new EVUS enrollment is also obligatory when one of the answers to any of the EVUS application questions changes.