Anti-dumping duty duration principle: duty stops after the statutory period unless a valid extension notification is issued. Definitive anti-dumping duty ceases at the end of the statutory limited period measured from the date of imposition; collection beyond that period is permissible only where a fresh notification validly extends the levy for a further full period or for an interim period while a timely review is pending, and any review-conclusion notified after expiry takes effect prospectively from its date of issue.