I received the same offer and have reviewed the terms and conditions. The terms and conditions state that the annual fee is non-refundable unless the account is canceled within 30 days of the bill in which the fee is billed. Also, the terms indicate that reward dollars that have not been sent to the Rapid Rewards program are canceled if your account is closed; however, it indicates only reward dollars that have not been sent to the Rapid Rewards program are canceled.
The terms appear to allow the canceling of the card after the credits have posted and the annual fee to be refunded within that 30 day window.