Hong Kong's payment of US dollars to China involves foreign exchange and cross-border settlement, which needs to be handled by multiple transit lines and banks, so it takes 2-3 working days or even longer.

After receiving US dollars, Hong Kong banks need to convert them into RMB and transfer the money to domestic banks through the cross-border payment system of China Bank. In this process, banks need to review relevant information and confirm the payee's account information and transaction amount to ensure the safety and accuracy of payment. In addition, banks also need to go through relevant foreign exchange procedures and settlement procedures, and it will take some time.