How to Change Date/Time Format Gnome Shell in Ubuntu 12.04

sudo gedit /usr/share/gnome-shell/js/ui/dateMenu.js


modify code in dateMenu.js as outlined in red (see image below) and save file



use dConf and goto org > gnome > shell > clock, and check the box to show date

new clock format

%A, %B %d, %Y  %I:%M %p

%A = Full weekday name
%B = Full month name
%d = Day of month
%Y = Year
%I = Hour in 12h format
%M = Minute (00 - 59)
%p = AM or PM

Reference:
http://www.cplusplus.com/reference/ctime/strftime/
Retrieved April 2013