PHP: How to get Sunday and Saturday

<?php
function getSaturdays($year,$month){ 
   	$last_day =  date('t',strtotime($year.'-'.$month));
	for ($x = 1; $x <= $last_day; $x++) { 
		$d1 = strtotime($year.'-'.$month.'-'.$x);
		if(date('D', $d1)=='Sat'){//all Saturdays
			$sat = strtotime(date('Y-m-d H:i:s', $d1).'+12 hours'); //Saturday
			$mon = strtotime(date('Y-m-d H:i:s', $sat).'+42 hours'); //Monday
			$out[]=array(date('Y-m-d H:i:s',$sat), date('Y-m-d H:i:s',$mon));
		}
	}
	return $out;
}

$days = getSaturdays(2016,9);
echo '<pre>'; print_r($days); echo '</pre>'; ?>