Mo. Rev. Stat. § 285.1055: Plan contribution start date — phase in permitted.

1. The board shall establish the plan so that individuals are able to begin contributing under the plan on or before September 1, 2025.

2. The board may, in its discretion, phase in the plan so that the ability to contribute first applies on different dates for different classes of individuals, including employees of employers of different sizes or types and individuals who are not employees; provided that, any such staged or phased-in implementation schedule shall be substantially completed on or before September 1, 2025.