USPS generally does not forward mail from USCIS to new address for security reason, it sends back the mail to USCIS. If USCIS has not already processed ur opt for shipment before u changed ur address at its site, it will send ur card to ur new address, if it has already shipped ur card, the card will be sent back, and they will send it to ur new address thereafter, it will increase ur opt delivery by few weeks.