N.Y.C. Admin. Code § 12-130: § 12-130 Office hours.

Except as otherwise provided by law, the office hours in all public offices of the city, and of all county offices within the city, shall be from nine o'clock antemeridian to five o'clock postmeridian. The head of a city office or department, or a county officer who comes within the foregoing provisions of this section, may adopt a rule that such office shall be closed to the public at four o'clock postmeridian, when in the judgement of such officer, the period between the hours of four o'clock postmeridian and five o'clock postmeridian is required for the performance of the work in such office. During the months of July and August the office hours of such offices shall be from nine o'clock antemeridian to four o'clock postmeridian if the head of the office or department so orders. The office hours of any such office, however, shall be from nine o'clock antemeridian to twelve o'clock noon on Saturday, provided that the commissioner of the department of finance may, in his or her discretion, adopt a rule that such office or department shall be closed to the public on Saturdays.