if you get a warning using the code-examples – then use this for code #0
$value = get_post_meta( $_REQUEST['post'], $title, true);
if ( $value ) $enforced_value = date('d/m/Y', (int)$value);
It converts $value from string to integer before feeding it to the PHP date function – which means you won’t get a warning.
Actually use this even though you don’t get a warning – you system-conf might change one day, and all of a sudden the warning will be there