Calculate the reponse time of your webpage, useful to check SQL request time.

Time.php

<?php

namespace app;

class Time
{
    private $startTime, $reponseTime;

    public function __construct(){
      $this->startTime = microtime(true);
    }

    public function end(){
      $this->reponseTime = microtime(true) - $this->startTime;
      $this->display();
    }

    public function display(){
      $html = '<div style="z-index:999;position:fixed;bottom:0;right:0;padding:20px;background-color:rgba(255,0,0,.5);color:white;">';
      $html .= '<span>Temps de réponse : ' . ($this->reponseTime) . ' seconds</span>';
      $html .= '</div>';
      echo $html;
    }

}

// --------------------------
//      HOW TO USE IT
// --------------------------


// --------------------------
//      To put at the top 
//      of your php file
// --------------------------

// If you don't have autoload
require_once('Time.php');

// Then

$t = new app\Time();

// --------------------------
//      To put at the end 
//      of your php file
// --------------------------

$t->end();