N.J. Stat. § 43:10-17
Any employee in the service of a county of the first class who has heretofore, in accordance with law, notified, or, at his option, within thirty days after permanent appointment notifies, the pension commission in writing that he does not desire to be bound by the provisions of this article, shall have no deductions made from his salary. In such event no pension shall be paid to him or his dependents under this article.
Any such county employee who, prior to June third, one thousand nine hundred and thirty-seven, declined to be bound by the provisions of this article, may, notwithstanding such declination, within six months after said date, become a member of said fund upon payment into the fund, in such manner as shall be determined by the pension commission, all arrears, with interest, as the pension commission shall determine to be due in order to give such employee the same standing as a member of said fund as all other members who joined said pension fund when the law providing for such fund became effective. The maximum rate of interest shall not exceed the average rate of earnings of the investments of said fund. The maximum length of time for the payment of arrears shall be five years from the date of the application to join the fund.
Any such county employee who, prior to June third, one thousand nine hundred and thirty-seven, declined to be bound by the provisions of this article, may, notwithstanding such declination, become a member of said fund upon written application, and the regular deductions from the salary of such employee shall commence upon the filing of such written application; provided, however, that neither such employee, nor his dependents, shall be entitled to any of the benefits of this article for a period of five years from the date of his acceptance into the fund as aforesaid.
N.J.S. § 43:10-17