An obligor shall make child support payments to the agency if the agency is enforcing a duty of child support under AS 25.25 or this chapter. The agency shall disburse that portion of a payment that exceeds the amount of money necessary to satisfy the obligor's immediate duty of support in accordance with state and federal requirements. The agency may characterize a support payment physically received by the agency through wage withholding during the last five business days of the month as having been received on the first day of the next calendar month if the agency determines that the payment was made in the course of regular wage withholding intended for the next calendar month. The agency shall credit money disbursed under this section toward satisfaction of the obligor's duty of support.