Lets get back on point, if you please...
Concerning the Cinnamon desktop of Mint 12 64 bit:
sudo apt-get update && sudo apt-get upgrade
After updating (see above) today (X-org), the clock in the lower right, permanently remains in the 24 hr setting.
The AM/PM setting of the clock on other desktops (Gnome, Gnome Classic, Mate, etc.) works just fine.
You can click on the clock applet, and then "set AM/PM", but the clock remains in the 24 hr setting. I can't get it to change to AM/PM.
EDIT: Upload image

- Screenshot-History64bit cinnamon.png (47.07 KiB) Viewed 2417 times