以前写的计划任务程序，发现有时和预期结果不同

<?phperror_reporting(E_ALL);ini_set('display_errors', '1');ignore_user_abort(true);header("Content-Type: text/html;charset=utf-8");date_default_timezone_set("PRC");class runjob{    static $myselftime = 50;    static $url = "http://127.0.0.1/to.php?pwd=123456789";    static $myself = "http://127.0.0.1/autorun.php";    static $urltime_H = 18;    static $urltime_i = 00;    function __construct()    {        if (!file_exists("runtime.txt"))        {            $fp = fopen("runtime.txt","w");            fwrite($fp,"");            fclose($fp);        }        if (!file_exists("time.txt"))        {            $fp = fopen("time.txt","w");            fwrite($fp,"");            fclose($fp);        }        if (file_exists("autorun.stop"))            exit();    }    function get_content($url)    {        $buf = parse_url($url);        $host=$buf['host'];        $path=$buf['path'];        if (isset($buf['query']))            $path .= "?" . $buf['query'];        $header = "GET " . $path . " HTTP/1.1\r\n";        $header .= "Host: " . $host . "\r\n";        $header .= "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n";        $header .= "Cache-Control: max-age=0\r\n";        $header .= "Accept-Encoding: gzip,deflate,sdch\r\n";        $header .= "Accept-Language: zh-CN,zh;q=0.8\r\n";        $header .= "User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.72 Safari/537.36\r\n";        $header .= "Connection: close\r\n\r\n";        $fp = fsockopen($host, 80, $errno, $errstr, 5);        if ($fp)        {            fputs($fp,$header);            fclose($fp);            return true;        }        else        {            return false;        }    }    function main()    {        $nowtime = $_SERVER["REQUEST_TIME"];        $time = file_get_contents("runtime.txt");        if ((self::$urltime_H == date("H")) && (self::$urltime_i == date("i")) && ($time != date("d")))        {            $this -> get_content(self::$url);            echo '运行成功';            $fp = fopen("runtime.txt","w");            fwrite($fp,date("d"));            fclose($fp);        }        $time = file_get_contents("time.txt");        if (($nowtime - $time) >= self::$myselftime)        {            sleep(self::$myselftime);            $this -> get_content(self::$myself);            $fp = fopen("time.txt","w");            fwrite($fp,$nowtime);            fclose($fp);        }    }}$job = new runjob();$job -> main();