macOS Time announcement -- how to speak a longer phrase
The solution:

(Optional) to get the plist in com.apple.speech.synthesis.general.prefs correct, set the structure as shown in my original question.  Or, simply delete that file and turn on the Time Announce checkbox in System Preferences (Dock &amp; Menu Bar, Clock).  That will re-create the file.

In the two defaults commands, use -dict-add (rather than -dict) so the commands won't delete any existing parameters.  At this point, the defaults command can be used to turn the time announcements on and off.  But, &quot;it's&quot; and &quot;o-clock&quot; are still missing.

Reboot, and &quot;it's&quot; and &quot;o'clock&quot; will return.  I still don't know what values TimeAnnouncementsPhraseIdentifier can take on, but ShortTime works (after a reboot).


But, my original idea of using defaults write to change the plist didn't work anyway.  The changes do not take effect without a reboot because the OS caches the plist.