Any construction, use or occupancy of any land, building or structure which has been lawfully commenced prior to the effective date of this chapter, pursuant to a valid special use permit, site plan approval, subdivision approval, variance, operating permit, certificate of use and/or building permit, may be completed and used in accordance with the conditions of said approval and plans on file with the applicable board, Code Enforcement Officer or Zoning Enforcement Officer, provided such construction and/or use is diligently pursued, and the building, structure or commencement of use of the land is completed within two calendar years of the adoption of this chapter or within the time period specified in the applicable approval and/or building permit, whichever is earlier.