Mo. Rev. Stat. § 82.815: Number of days city offices to remain open, how set.

In any city having a population of over five hundred fifty thousand inhabitants, the governing body by order entered of record may authorize all city and county offices, except the sheriff's office, to be open not more than five days each week. The board of aldermen, after entering such an order, may require any office to be open six days a week when public convenience requires.