The applicant may apply for and the Planning Board may grant extensions of such preliminary approval for additional periods of at least one year but not to exceed a total extension of two years, provided that if the design standards have been revised by ordinance, such revised standards shall govern.

In the case of a site plan for a planned unit development, the Planning Board may grant the rights referred to above for such period of time longer than three years as shall be determined by the Planning Board to be reasonable, taking into consideration the number of dwelling units and nonresidential floor area permissible under preliminary approval, economic conditions and the comprehensiveness of the development. The applicant may apply for thereafter, and the Planning Board may thereafter grant, an extension of preliminary approval for such additional period of time as shall be determined by the Planning Board to be reasonable, taking into consideration the number of dwelling units and nonresidential floor area permissible under preliminary approval, the potential number of sections awaiting final approval, economic conditions and the comprehensiveness of the development, provided that if the design standards have been revised, such revised standards shall govern.