Section 21. The developer shall have the duties imposed on the managing entity by this chapter and the powers set forth in clauses (1) to (11), inclusive, of subsection (a) of section twenty until a managing entity is provided or the developer and his affiliates own no estate or interest in the time-share property, whichever first occurs. Thereafter, if there is no managing entity and the number of time-shares in the time-share property is twelve or fewer, the time-share owners shall have said powers subject to any provisions of the time-share instrument relating to the manner of the exercise thereof and shall have the responsibilities and liabilities of an association for the purposes of sections twenty-four and twenty-five. To the extent that the time-share instrument is silent with respect to the manner of exercise of any of said powers, the time-share owner may exercise said powers only by unanimous action.