Board of Appeals decision. No appeal, application or petition which has been unfavorably and finally acted upon by the Board of Appeals shall be favorably and finally acted upon within two years after the date of such unfavorable action unless all but one of the members of the Planning Board consent to a re-petition after notice is given to parties in interest of the time and place of the proceedings to consider consent and the Board of Appeals finds specific and material changes in the conditions upon which the previous unfavorable action was based, describes such changes in its records and similarly consents.