Retail/Wholesale Fulfilment Days are the weekdays on which your kitchen delivers stock to this location. They decide which dates appear on the calendar of the location's Retail Menu, which dates a wholesaler can order stock for, and which dates the Retail Dropoff Report covers.

A weekday is greyed out (disabled) when the kitchen itself does not fulfil retail/wholesale on that day - see Kitchen Locations > edit kitchen > Retail / Wholesale fulfilment ("Weekdays this kitchen fulfils retail and wholesale orders"). Enable the day on the kitchen first, then on the location. New locations start with all allowed days ticked.