Joomla! 1.5 date is stored in the file "language".ini. For example, for English, it is <Joomla! home>/en-GB/en-GB.ini.

You can change the date format by edit the values "DATE_FORMAT_LCx". By default, the date is in international format (for example, Thursday, 31 January 2008 18:30).

To change to standard US format (for example, Thursday, January 31, 2008, 06:30 PM), make the following changes:

DATE_FORMAT_LC=%A, %B %d, %Y
DATE_FORMAT_LC1=%A, %B %d, %Y
DATE_FORMAT_LC2=%A, %B %d, %Y %I:%M %p
DATE_FORMAT_LC3=%B %d, %Y
DATE_FORMAT_LC4=%m.%d.%y
DATE_FORMAT_JS1=m-d-y
%Y-%M-%D=%Y-%M-%D
%A, %B %E=%A, %B %e

These are the formats for the time

%H:%M = 00:00 through 23:59
%k:%M = 0:00 through 23:59

%I:%M %P = 00:00 am through 23:59 pm (I = upercase i)
%l:%M %P= 0:00 am through 23:59 pm (l = lowercase L)

(Note that %P will print the lowercase am/pm indicator for your locale, which may be blank.)

%I:%M %p = 00:00 AM through 23:59 PM (I = upercase i)
%l:%M %p= 0:00 AM through 23:59 PM (l = lowercase L)

Joomla! uses standard Linux date format codes. These codes are listed at the following link: http://nl3.php.net/manual/en/function.date.php

By: http://docs.joomla.org/How_do_you_change_the_date_format%3F