Dine with Shamu - late booking

[Portugal1000]

Will be there from 11th August to 1st September. Brothers family coming for two weeks within that period but not sure yet. So two questions. Has anyone booked Dine with Shamu when they are actually in Orlando? Was thinking it would be nice this year not to have too many things booked up in advance, a more go with the flow experience. Also, if I did book a date, are you able to change it when you are there to another date?
Thanks