In the case of a subdivision for a planned development of 50 acres or more or major conventional subdivision or site development plan for 150 acres or more, the Approving Authority may grant the rights referred to herein for such period of time, longer than two years, as shall be determined by the Approving Authority to be reasonable taking into consideration: (a) the number of dwelling units and nonresidential floor area permissible under final approval, (b) economic conditions, and (c) the comprehensiveness of the development. The applicant may apply for thereafter, and the Approving Authority may thereafter grant, an extension of final approval for such additional period of time as shall be determined by the Approving Authority to be reasonable taking into consideration (a) the number of dwelling units and nonresidential floor area permissible under final approval, (b) the number of dwelling units and nonresidential floor area remaining to be developed, (c) economic conditions, and (d) the comprehensiveness of the development.