Welcome to cruise-chat! Using the credit card is my preferred option since I don't have to worry about it. I let the cruise line bill it and then pay it off when the bill arrives. But that is my choice. As to your question - sure, you can pay down part or all of your shipboard account anytime during the cruise. They do not send the final charges to your credit card company until after you have left the ship. I suggest doing this prior to the last morning, when it will be a mob scene at the guest relations desk. Going down during the afternoon of the last day and paying off some of your bill will be the best choice.