Provided that, in the case of goods imported overland, the time of entry of the goods for home use shall be deemed to be the time when the duty thereon is paid.

(2) Except where otherwise provided in the Fourth Schedule, and subject to section 74, export duty shall be paid at the rate in force at the time when the goods liable to the duty are entered for export:

Provided that where export duty is imposed, or the rate of existing export duty is varied, between the time goods are entered for exportation and the time of exportation of the goods, export duty shall be paid at the rate in force at the time of exportation of the goods.

(3) Where, in accordance with section 27 (3), goods are entered before the arrival at the port of discharge of the aircraft or vessel in which the goods are imported, the duty upon the goods shall be paid at the rate in force at the time of arrival of the aircraft or vessel at the port or place of discharge.