The certificate referred to in sub-section (1) of section 8 shall be issued or renewed for such period, not exceeding five years, as may be prescribed:
Provided that where validity of certificate on inventory of hazardous material expires at a time when a ship is not in the port in which it is to be surveyed, the Administration may extend the period of validity of such certificate and this extension shall be granted only--
(a) for the purpose of allowing the ship to complete its voyage to the port in which it is to be surveyed; or
(b) in cases where it appears proper and reasonable to the Administration to do so:
Provided further that no certificate shall be extended for a period longer than three months, and a ship to which an extension is granted shall not, on its arrival on the port in which it is to be surveyed, be entitled by virtue of such extension to leave that port without having the certificate renewed.