25 CFR §18.306

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