In the case of a subdivision or site plan for a planned development of 50 acres or more, conventional subdivision or site plan for 150 acres or more, or site plan for development of a nonresidential floor area of 200,000 square feet or more, the Board may grant the rights referred to in paragraph F above for such period of time, longer than two years, as shall be determined by the Board to be reasonable taking into consideration 1) the number of dwelling units and nonresidential floor area permissible under final approval, 2) economic conditions and 3) the comprehensiveness of the development. The developer may apply for thereafter, and the Board may thereafter grant, an extension of final approval for such additional period of time as shall be determined by the Board to be reasonable taking into consideration 1) the number of dwelling units and nonresidential floor area permissible under final approval, 2) the number of dwelling units and nonresidential floor area remaining to be developed, 3) economic conditions and 4) comprehensiveness of the development.