I just did this 2 weeks ago on Liberty OTS. I did not know what date I could do, so I did the 200 down (much of which was later refunded) and called later to book. You have 7 days to do so. Interesting thing is it was for a balcony and 250 cash, but when I called they told me I had been changed to 500 cash. Perfect! I lost $570 in the casino, so they give me 500 back and I get a cruise for $70.00 plus taxes and port charges.