12-Hour Time Formating Fix

Fixed the Time format to 12-hour format because it is followed by Ante meridiem and Post meridian symbols. It caused strange Time format like "20 AM" and caused the field to save to "empty" because of that the next time you updated the post/page.

![20pm](https://f.cloud.github.com/assets/339914/1141204/50da3ada-1caf-11e3-9e53-384cf3e0b6fc.jpeg)

Signed-off-by: Baki Goxhaj <banago@gmail.com>