Such retirements, if made, shall be made immediately after a period fixed by the bylaws of the association for the declaration and payment of dividends of earnings, and the association shall, at least sixty days before so retiring any shares, send written notice to each person shown by the books of the association to be an owner of such shares, mailed to such person’s last-known address, which notice shall inform such persons of the intent of the association to make the retirement on a designated date.