$client = new SoapClient($wsdlUrl);
$backclickStatisticRequest = new StdClass();
$backclickStatisticRequest->mandatorId = 0;
$backclickStatisticRequest->newslettersInPeriod = new StdClass();
$backclickStatisticRequest->newslettersInPeriod->newsletterListId = 1;
$backclickStatisticRequest->newslettersInPeriod->timePeriod = new StdClass();
date_default_timezone_set('Europe/Berlin');
$backclickStatisticRequest->newslettersInPeriod->timePeriod->startTime = mktime(13, 10, 0, 10, 30, 2012);
$backclickStatisticRequest->newslettersInPeriod->timePeriod->endTime = mktime(13, 19, 0, 10, 30, 2012);
try {
  $result = $client->BackclickStatistic($backclickStatisticRequest);
  var_dump($result);
} catch (Exception $e) {
  echo "Fehler aufgetreten: " . $e->getMessage() . "\r\n";
}