Change the days and times displayed in Calendar on Mac
Calendar has several options for customising how many days and hours are shown. You can customise Week view to show all seven days of the week or just Monday to Friday. You can customise Day and Week views so that the Calendar window shows from 6 to 24 hours of events per day, and you can mark when your day starts and ends.
In the Calendar app on your Mac, choose Calendar > Settings.
Click General, then choose options from the pop-up menus.
To choose whether times are shown in 12-hour or 24-hour time format, change Language & Region settings.