(a) in the case of any import made by any individual for his personal use or by Government or by any educational, research or charitable institution or hospital, within one year;

(b) in any other case, within six months, from the relevant date, serve notice on the person chargeable with the duty which has not been levied or which has been so short- levied or to whom the refund has erroneously been made, requiring to him to show cause why he should not pay the amount specified in the notice:"] Provided that where any duty has not been levied or has been short- levied or has been erroneously refunded by reason of collusion or any wilful miss- tatement or suppression of facts by the importer or the exporter, or the agent or employee of the importer or exporter, the provisions of this sub- section shall have effect 4[ as if] for the words 3[ one year" and" six months"] the words" five years" were substituted. 5[ Explanation.-- Where the service of the notice is stayed by an order of a Court, the period of such stay shall be excluded in computing the aforesaid period of one year or six months or five years, as the case may be."]

(a) in a case where duty is not levied, the date on which the proper officer makes an order for the clearance of the goods;

(b) in a case where duty is provisionally assessed under section 18, the date of adjustment of duty after the final assessment thereof;

(c) in a case where duty has been erroneously refunded, the date of refund;

(d) in any other case, the date of payment of duty.