Entry into and withdrawal from participation in a common trust fund may occur only on a valuation date, or, if provided by the plan, within 2 business days after a valuation date. Participation shall be based on the valuation as of the valuation date associated with the entry or withdrawal. When participation is withdrawn from a common trust fund, the trust company may make distribution in cash, ratably in kind, or both, but all distributions associated with a valuation date shall be made in the same way.