25 CFR §18.207

1. (a)An amendment may not become effective sooner than 180 days after the date of approval by the Department.
2. (b)If an amendment is deemed approved through inaction by the Department, then the amendment will become effective 180 days after it is deemed approved.
3. (c)The amendment will apply only to the estate of a decedent who dies on or after the effective date of the amendment.