Expiration. A final development plan approval shall be deemed to authorize only the particular uses specified in such approval and shall expire if substantial construction of the final development plan is not commenced within two years from the date of the final signature of the plan maps. The Planning Board may, at its discretion, after conducting a public hearing, grant an extension to an approved final development plan. The applicant shall submit a written request 60 days prior to the date of expiration of the final development plan approval, requesting an extension for a specified time and the reason therefor. In granting the extension, the Planning Board may require revision of the previously approved final development plan to comply with current regulations and conditions. The Planning Board shall render a decision, in writing, to the applicant and the other appropriate agencies within 45 days of closing the public hearing. The time within which the Planning Board must render its decision may be extended by mutual consent of the applicant and the Planning Board.