script para medir o tempo gasto do arquivo/sistema.

tempoGasto.php

<?php
  $time = microtime(TRUE); 
  function formatPeriod($endtime, $starttime)
  {
    $duration = $endtime - $starttime;
    $hours = (int) ($duration / 60 / 60);
    $minutes = (int) ($duration / 60) - $hours * 60;
    $seconds = (int) $duration - $hours * 60 * 60 - $minutes * 60;

    return ($hours == 0 ? "00":$hours).":".($minutes == 0 ? "00":($minutes < 10? "0".$minutes:$minutes)).":".($seconds == 0 ? "00":($seconds < 10? "0".$seconds:$seconds));
  }
  
  //SCRIPT PHP A SER PROCESSADO
  
  echo formatPeriod(microtime(TRUE),$time);