I don't really understand your question.
Here, I rewrote your code so it's more readable:
$searchAr = array('0','-',':');
$newValue = "000-00-00 00:00";
if ( str_replace( $searchAr, $newValue ) == '')
The method definition of str_replace is
mixed str_replace ( mixed $search , mixed $replace , mixed $subject [, int &$count ] )
Meaning "search the values of $search in $subject and replace it with $replace".
Your code seems to say "search the values of $searchAr and replace it with $newValue in..."
I think there is a parameter missing there.. no?
You want to replace what with what in what?