N.Y. Real Prop. Tax Law § 489-hhh

§ 489-hhh. Extension of time for completion. Where an applicant has\nreceived a certificate of eligibility but has not completed or will not\nbe able to complete the construction or reconstruction work within\nthirty-six months, the board shall, upon application, extend to\nforty-eight months, from the time of issuance of such certificate, the\ntime for completion of the construction or reconstruction work; provided\nthe applicant has completed not less than two-thirds of the work as\nspecified in the certified plans previously filed with the application\nat the time of such application for extension.\n