Here’s the way to set it up:

• Open System Preferences by clicking the Apple icon in the upper left corner of your screen.
• Select “System Preferences” from the menu that appears.
• Click “Date & Time” in “System Preferences” in MacOS Catalina or earlier. 
• Click “Dock & Menu Bar” on MacOS 11 Big Sur or later.
• If you are running Catalina or earlier, click the “Clock” tab in the “Date & Time” preferences.
• In Big Sur or later, scroll down the “Dock & Menu Bar” sidebar and click “Clock” button.

• When you have “Clock” preferences, place a checkmark next to “Announce Time.”
• Using the drop-down menu, you can customize it if you want your Mac to announce the hour, half-hour, or quarter-hour time.
• Example, if you select “On the quarter-hour,” you will hear the announcements at 2:00 p.m., 2:15 p.m., 2:30 p.m., and 2:45 p.m.
• The voice is going to say, “It’s two o’clock” or “It’s two forty-five.”

• Press the “Customize Voice” button to change the voice that speaks the time out loud.
• You can choose a male or female voice on the screen, and you can also adjust the speech rate.
• As long as you have the volume of your system turned up, you’ll hear the time you’ve spoken at the intervals you set.