How to stop announcing the time on macOS Big Sur 11.0.1
You can disable this in System Preferences -&gt; Dock &amp; Menu Bar -&gt; Clock

The setting is stored in ~/Library/Preferences/com.apple.speech.synthesis.general.prefs.plist:
$ plutil -p com.apple.speech.synthesis.general.prefs.plist
{
  &quot;SpokenUIUseSpeakingHotKeyFlag&quot; =&gt; 1
  &quot;TimeAnnouncementPrefs&quot; =&gt; {
    &quot;TimeAnnouncementsEnabled&quot; =&gt; 1
    &quot;TimeAnnouncementsIntervalIdentifier&quot; =&gt; &quot;EveryHourInterval&quot;
    &quot;TimeAnnouncementsPhraseIdentifier&quot; =&gt; &quot;ShortTime&quot;
    &quot;TimeAnnouncementsVoiceSettings&quot; =&gt; {
      &quot;CustomVolume&quot; =&gt; 0.5
    }
  }
}

You can use any Plist editor (or defaults) to change the setting, it may require a restart (or killing the Dock) though to get activated.