Sorry, misread the topic...
Have tried to change different settings to try and get 12h clock on the Gemini app-bar, and can't seem to make that happen... But on the Cosmo it DOES follow the setting in the settings for time for Android.
So other than "upgrading" to a Cosmo, it might look like you are out of luck. And I doubt that getting the app-bar to display a 12h clock actually warrants that upgrade... And if you WERE to upgrade, I would recommend the Astro instead