求助DingTalkClient 类 setStartTime 参数 处理问题

1、 php代码
            $stime = (string) strtotime('2017-11-01 08:00:00')*1000 ; //"14 9667 8400 000";
            //$stime = "1509494400000" ;
            $endtime = strtotime('2017-11-10 08:00:00')*1000; //"1496678400000";
            
            $c = new DingTalkClient;
            $req = new SmartworkBpmsProcessinstanceListRequest;
            $req->setProcessCode("PROC-B126B388-D2A1-4143-926A-2C74824559A3");
            $req->setStartTime($stime);
            $req->setEndTime($endtime);
            $req->setSize("10");
            $req->setCursor("0");
            $resp = $c->execute($req, $access_token);



2、使用
   $stime = (string) strtotime('2017-11-01 08:00:00')*1000 ; //"


   返回
SimpleXMLElement Object([code] => 40[msg] => Missing required arguments:start_time[request_id] => 2imht4yakld0)使用 $stime = "1509494400000" ; 返回正常（成功）
3、 求助，何解？ 哪里错了？