The working days in Outlook by default is Monday to Friday, but you can change to any other days. For example, if you have a part-time job and work only from Monday to Thursday, you may want to change the working days in the calendar so your co-workers will know when they arrange a meeting.
Step 1: Click the "File" tab in the ribbon;
Step 2: Click "Options" from the left menu;
Step 3: Click "Calendar" in the "Outlook Options" window;
Step 4: In the "Work time" section, check the days as working days. Click "OK" at the bottom to close the window;
Step 5: Close and re-open the calendar, you will find Friday has the same color as a holiday in the "Week" view.