Hi Lindsay,
Yes, that's correct ๐ However, we would say that there is always the possibility of the itinerary having to be changed for various reasons, as can sometimes happen, so generally we'd advise you book when you arrive so you can sure that nothing is going to change.
However, it's totally up to you if you would like to book in advance, and those are the planned dates for the excursions ๐
Thanks,
Vickie