<?
list($usec, $sec) = explode(" ", microtime());
$script_start = (float) $sec + (float) $usec;

##########################################

As instruções abaixo devem ser inseridas no final da página:

list($usec, $sec) = explode(" ", microtime());
$script_end = (float) $sec + (float) $usec;
$elapsed_time = round($script_end - $script_start, 5);
echo $elapsed_time;
?>