§ 73. Fiscal year; departmental estimates. The fiscal year of the city shall commence on the first day of January. On or before the first day of November in each year all heads of departments and officers empowered by law or by city ordinance to control or authorize expenditures shall furnish to the mayor estimates in writing of the amount of expenditures for the next fiscal year in their respective departments or offices, including a statement of the salaries of all their subordinates, which estimates the mayor shall lay before the board of estimate and apportionment at its first meeting thereafter, and the same shall be entered in its minutes.