Missouri Revised Statutes Title I. Laws and Statutes § 1.130. Effective date of laws

(1) A law necessary for the immediate preservation of the public peace, health or safety, which emergency is expressed in the body or preamble of the act and which is declared to be thus necessary by the general assembly, by a vote of two-thirds of its members elected to each house the vote to be taken by yeas and nays, and entered on the journal, or a law making an appropriation for the current expenses of the state government, for the maintenance of the state institutions or for the support of public schools, takes effect as of the hour and minute of its approval by the governor; which hour and minute may be endorsed by the governor on the bill at the time of its approval;

(2) In case the general assembly, as to a law not of the character herein specified, provides that the law takes effect on a date in the future subsequent to the expiration of the period of ninety days herein mentioned the law takes effect on the date thus fixed by the general assembly;

(3) In case the general assembly provides that any law takes effect as provided in subdivision (1) of this section, the general assembly may provide in such law that the operative date of the law or parts of the law takes effect on a date subsequent to the effective date of the law.