Hello @DarrylLawrence, Darryl,
instead of creating a calendar with SMC, I would rather recommend you to create it with the tool named Calendar Editor. This will create the appropriate calendar file and will make it available for SMC, so you can select it to schedule any flow.
So, in short, probably better to keep calendar creation and flow scheduling separate, calendar on Calendar Editor and Flow Scheduling on SMC. That is what I do.
Of course, you will need the permissions on the calendars folder, to generate the appropriate file (calendar).