Deferred export duty payment permitted by notification; interest charged on unpaid duty at government fixed rate. Section 51 is renumbered as sub-section (1) and a proviso permits the Central Government, by notification, to allow certain classes of exporters deferred payment of export duty or charges in the manner provided by rules. A new sub-section (2) requires exporters who fail to pay such duty by the rulespecified due date to pay interest on unpaid or short-paid duty at a rate fixed by the Central Government by notification, subject to prescribed minimum and maximum limits.