How do you change the date format?
From Joomla! Documentation
The "J1.5" namespace is an archived namespace. This page contains information for a Joomla! version which is no longer supported. It exists only as a historical reference, it will not be improved and its content may be incomplete and/or contain broken links.
The date format information for Joomla! 1.5 is stored in the file <Joomla! home>/language/<your language>/<your language>.ini. For example, for English, it is <Joomla! home>/en-GB/en-GB.ini.
To change the date format, find and 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)
...and for the day
d - Day of the month, two digits with leading zeros - 01 to 21 D - Day in text, three letters - Sun through Sat j - Day of the month, one or two digits without leading zeros - 1 to 31 l (lowercase L) - Day in text, complete word - Sunday through Saturday
Joomla! uses standard Linux date format codes. A complete reference is avaialable in the PHP Manual.