Section 70. The city council shall fix suitable times for regular meetings. The mayor, the president of the city council or any two members thereof may at any time call a special meeting by causing a written notice, stating the time of holding such meeting and signed by the person calling the same, to be delivered in hand to each member, or left at his usual dwelling place, at least six hours before the time of such meeting. Meetings of the city council may also be held at any time when all the members of the council are present and consent thereto.