Go to your language file. For example: /administrator/language/en-GB/en-GB.ini and change line 11:
DATE_FORMAT_LC2=%A, %d %B %Y %H:%M to DATE_FORMAT_LC2=%A, %d %B %Y
If this doesn’t work try this: http://forum.joomla.org/viewtopic.php?f=470&t=347359&start=0