Support 12h or 24h time display format
This a diplication of an LP issue at :https://bugs.launchpad.net/ubuntu-clock-app/+bug/1388931
Updating this bug based on the comments and dupes.
There should be a setting in the Time & Date settings control panel to select 12 or 24 hour display format. This should be honored in the indicator, greeter and clock app.
gsetting com.canonical.indicator.datetime time-format controls this