How can I append date and time to node titles?
This will do for you

function modulename_node_presave($node) {
      if($node-&gt;type == 'node_type_machine_name') {
        $new_date = date("DMY_hms", time());
        $node-&gt;title = $node-&gt;title."_".$new_date;
      }
}