Unless exercised within a period designated by the commission, but not exceeding one year from the grant thereof, exclusive of any delay due to the order of any court, or the failure to obtain any grant or consent, authority conferred by a certificate of convenience and necessity issued by the commission shall be null and void; but the beginning of the construction of the road, line, system or works of such utility, in good faith within the time prescribed by the commission, and the prosecution of the same with reasonable diligence, shall constitute a compliance with such certificate.