If a user does not understand 'Minimum scheduling notice' and 'Date range' they can create a scenario where the calendar shows no availability. Specifically a user can set the following:

Minimum scheduling notice: 1 day

Date range: 1 day

This makes it impossible to for there to be an available day.

There should be validation to ensure that:

'Date range' is always a time interval greater than 'Minimum scheduling notice'