43 CFR §3137.85

1. (a)The effective date of an initial participating area is the first day of the month in which you complete a well meeting the productivity criteria, but no earlier than the effective date of the unit.
2. (b)The effective date of a modified participating area or modified allocation schedule is the earlier of the first day of the month in which you file the proposal for a modification or such other effective date as may be provided for in the unit agreement and approved by the BLM, but no earlier than the effective date of the unit.