When 6 years shall have elapsed from the date of the first summoning, under section 6, of persons to the Legislative Council, or when the Registrar General of the Colony shall have certified, by writing under his hand to be published in the Government Gazette, that the population of the Colony has, to the best of his knowledge and belief, exclusive of aboriginal natives, attained to 60 000 souls, whichever event shall first happen, this Part shall come into operation, provided that the Governor in Council shall have power, by proclamation in the Government Gazette, to further postpone the operation of this Part for any period not exceeding 6 months.