Limitation period for refund claims governs filing deadlines with special computation rules for exceptions and provisional payments. Limitation for refund applications is generally one year from date of payment, but where an ad hoc exemption order is issued the period runs from the date of that order; where refundability arises from a judicial or appellate direction it runs from the date of that direction; for provisional payments the period runs from the date of adjustment after final assessment or from the date of reassessment; and for persons other than the importer the date of payment is the date of purchase. The one year limitation does not apply to duties paid under protest.