43 C.F.R. § 3137.85
What is the effective date of a participating area?
(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.
(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.