How strange, this is what I see on FAQ
Search Saga Ocean Cruise FAQs | Travel & Service Information
You can change or amend your choice of excursions up to approximately 7 days before departure. After that please visit the Explore Ashore Desk when onboard to make any changes. Please note you can cancel a tour free of charge (unless specifically stated in the tour description) up to 48 hours prior to that port of call. After that you will still need to pay the full excursion cost (unless you have a medical exemption certificate from the Ship’s doctor).
The operation of excursion is subject to them reaching minimum required numbers. If we need to cancel a tour for that reason you will be offered an alternative tour where possible or a full refund.