Use this window to register the scheduled working hours for a Day Type. A Day Type is then later on connected to a Schedule and the Schedule is connected to a Calendar. The final result is that all days in a specific Calendar are of a defined Day Type.
A Day Type defines all scheduled working hours from midnight until midnight. Each period of working time is connected to a Period. Basic data for this is defined in the Period window.
If you have periods that runs over midnight, e.g. night shifts. Those are defined by connecting Day Types (in a schedule) that have the same period and that ends at midnight (first Day Type) and starts at midnight (next Day Type).