This chapter shall become effective on the date of its approval (date), provided, however, that all buildings for which permits have been obtained and the construction of which has begun, or for which a contract or contracts have been let pursuant to a permit issued prior to (date of adoption) may be completed and used in accordance with the plans on which said permit was granted, and provided further that all permits issued within 60 days prior to the approval of this chapter for buildings or uses which do not conform to the provisions of this chapter are hereby declared void if at the time of the approval of this chapter no substantial construction of such building shall have been made or no contracts have been let pursuant to such permit.