IF(
  OR(
    VALUE( MID( TEXT( ***date/time*** - TZoffset ), 12, 2 ) ) = 0,
    VALUE( MID( TEXT( date/time - TZoffset ), 12, 2 ) ) = 12
  ),
  "12",
  TEXT( VALUE( MID( TEXT( date/time - TZoffset ), 12, 2 ) )
   -
   IF(
     VALUE( MID( TEXT( date/time - TZoffset ), 12, 2 ) ) < 12,
     0,
     12
   )
  )
)
& ":" &
MID( TEXT( date/time - TZoffset ), 15, 2 )
& ":" &
MID( TEXT( date/time - TZoffset ), 18, 2 )
& " " &
IF(
  VALUE( MID( TEXT( date/time - TZoffset ), 12, 2 ) ) < 12,
  "AM",
  "PM"
)

<apex:page standardController="Opportunity" id="pg">
    <apex:outputField value="{!opportunity.createddate}" id="st">
        <script type="text/javascript">
        (function(){
            var fd = document.getElementById("pg:st");
            fd.innerHTML = field.innerHTML.substring(field.innerHTML.indexOf(' '));
        })();
        </script>
    </apex:outputField>
</apex:page>