The commission shall file with the inspector of buildings or other duly delegated authority its certificate of approval or rejection of all plans submitted to it for review. No work shall begin until the certificate has been filed, but, in the case of rejection, the certificate is binding upon the inspector of buildings or other duly delegated authority, and no permit shall be issued in that case. The failure of the commission to act within forty-five (45) days from the date of application filed with it, unless an extension is mutually agreed upon by the applicant and the commission or unless the commission makes a finding of fact that circumstances require additional time for study up to a maximum of ninety (90) days, is deemed to constitute approval.