Change the menu bar clock format on Mac
On your Mac, a clock is always displayed in the menu bar. In addition to showing the current time and date, you click it to open Notification Center.
Set up the menu bar clock
On your Mac, choose Apple menu
in the sidebar. (You may need to scroll down.)Go to Menu Bar Only, then click Clock Options.
Below Date, set the options you want for the date display.
Show date: Click the “Show date” pop-up menu, then choose when to display the date (When Space Allows, Always, or Never).
Show the day of the week: Display the day of the week before the date.
Below Time, set the options you want for the time display.
Style: Choose a digital or analog clock. If you choose an analog display, the remaining options for the time display are unavailable.
Show AM/PM: Display AM or PM following the time.
Flash the time separators: Turn the characters that separate the time components on and off at one-second intervals.
Display the time with seconds: Display the time as Hours:Minutes:Seconds. If this option is turned off, the time displays as Hours:Minutes.
Announce the time: If you turn on this option, click the Interval pop-up menu, then choose when to announce the time (on the hour, on the half hour, or on the quarter hour).
Customize Voice: If you turned on “Announce the time,” click Customize Voice to choose a voice and set the speaking rate and volume.
If the menu bar clock is dimmed
The menu bar clock is dimmed when a Focus is active and the Focus status menu 
isn’t shown in the menu bar. To prevent the clock from being dimmed, change the menu bar settings to show the Focus status menu.
On your Mac, choose Apple menu
Click the Focus pop-up menu, then choose Always Show in Menu Bar or Show When Active.
To learn how to use a 24-hour time format or change your time zone, see Change Date & Time settings.