PHP calculate page execution time

<?php
$t = new executeTime;
  
phpinfo();
  
class executeTime{
    private $microtime;
    public function __construct(){
        $this->microtime = microtime(true);
    }
  
        public function getNow(){
                $this->__dectruct();
        }
  
    public function __destruct(){
        if (empty($_SERVER[&#39;REQUEST_TIME_FLOAT&#39;]))
            echo &#39;<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次执行时间：&#39;, microtime(TRUE) - $this->microtime, &#39;秒</div>&#39;;
        else
            echo &#39;<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次执行时间：&#39;, microtime(TRUE) - $_SERVER[&#39;REQUEST_TIME_FLOAT&#39;], &#39;秒</div>&#39;;
    }
}