63.—For the purposes of section 62(1)(f) , the day that is to be specified in a notice of termination is the last day of—

( a) the period which, by reason of Chapter 3, is the period of notice to be given by that notice of termination, or

( b) such longer period of notice as the landlord or tenant (as appropriate) chooses, subject to section 65(4) , to give by that notice of termination.