29 C.F.R. § 20.57
Accrual of interest
Interest shall accrue from the date on which notice of the debt and the interest requirements is first mailed or hand-delivered to the debtor, using the most current address that is available to the agency.
Interest shall accrue from the date on which notice of the debt and the interest requirements is first mailed or hand-delivered to the debtor, using the most current address that is available to the agency.