time_sleep_until and filesize not working?

i use this php code to grab a web page. i use time_sleep_until but it does not seem to even exist?
filesize comparison seems to be ignored too? (i have tested and it did give correct file size.)

while(1)
{
	$simpledate=date('Y-m-d H:i:s');
	$date=strtotime($simpledate);
	$year=date('Y',$date);
	$month=date('m',$date);
	$day=date('d',$date);
	$hour=date('H',$date);
	$minute=date('i',$date);
	$sec=date('s',$date);
	$tomorrow=mktime(0, 0, 0, date("m"), date("d")+1, date("y"));

    if ($hour>23) {
      $str=$tomorrow.' 9:10:30';
      $timestamp=strtotime($str);
      time_sleep_until($timestamp);
    }
    $oldsize=filesize('todays11');

	$myURL ="http://example.com/";
	$ch = curl_init();	
	curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
	curl_setopt($ch, CURLOPT_URL, $myURL);
	curl_setopt($ch, CURLOPT_HTTPGET, TRUE); 
	curl_setopt($ch, CURLOPT_FOLLOWLOCATION, TRUE);
	$content=curl_exec($ch);
	
	$myfile='todays11';
	$f=fopen($myfile,'w') or die ('cant open file');
	fwrite($f,$content);
	fclose($f);
        $newsize=filesize($myfile);
        if(floor($newsize/100)==floor($oldsize/100) || $newsize<10) { // try again
	  sleep (60);

        } else {
        if($minute<50)$minute=floor($minute/10)*10+10;
        else {$hour=$hour+1; $minute=00;}
        $str=$year.'-'.$month.'-'.$day.' '.$hour.':'.$minute.':30';
        $timestamp=strtotime($str);
        time_sleep_until($timestamp);
       }
}