Mo. Rev. Stat. § 56.825: Retirement of member, application to board — payments to begin, when.

Any member may retire at any time after the end of the month during which the member becomes eligible to retire under the provisions of section 56.814 and upon the member's submission of a written application to the board setting forth at what time, not less than thirty days nor more than ninety days subsequent to the execution and filing of the application, the member desires to be retired. The payment of the annuity, subject to the provisions of section 56.840, shall begin as of the first day of the calendar month coincident with or next following the date specified by the member.