By clicking the option Business hours and Custom settings you get to edit the default business hours of your customers. The times entered here are applied to all customers that do not explicitly have different business hours set on their customer detail pages – see Business hours. The editing is analogous.
By clicking on Organization default you can see the company-wide default settings.
Note for administrators: These settings can be defined in the organization options as organization default for all users (see
Organization-wide settings and their effects). Users can overwrite these individually as described here.