PHP 毫秒时间戳转 成日期格式

最近在做京东的CPS，订单返回时间是毫秒时间戳，我想把它转成日期格式

   public function getMsecToMescdate($msectime)
    {
        $msectime = $msectime * 0.001;
        if(strstr($msectime,'.')){
            sprintf("%01.3f",$msectime);
            list($usec, $sec) = explode(".",$msectime);
            $sec = str_pad($sec,3,"0",STR_PAD_RIGHT);
        }else{
            $usec = $msectime;
            $sec = "000";
        }
        $date = date("Y-m-d H:i:s.x",$usec);
        return $mescdate = str_replace('x', $sec, $date);