https://www.bankersonline.com/regulations/scra-527(b) IMPLEMENTATION OF LIMITATION-
(1) WRITTEN NOTICE TO CREDITOR- In order for an obligation or liability of a servicemember to be subject to the interest rate limitation in subsection (a), the servicemember shall provide to the creditor written notice and a copy of the military orders calling the servicemember to military service and any orders further extending military service, not later than 180 days after the date of the servicemember's termination or release from military service.
(2) LIMITATION EFFECTIVE AS OF DATE OF ORDER TO ACTIVE DUTY- Upon receipt of written notice and a copy of orders calling a servicemember to military service, the creditor shall treat the debt in accordance with subsection (a), effective as of the date on which the servicemember is called to military service.