$loadbegintime = microtime();
$loadbeginarray = explode(" ", $loadbegintime);
$loadbegintime = $loadbeginarray[1] + $loadbeginarray[0];
$loadendtime = microtime();
$loadendarray = explode(" ", $loadendtime);
$loadendtime = $loadendarray[1] + $loadendarray[0];
$total_script_time = $loadendtime - $loadbegintime;
echo "".round($total_script_time , 6) ."segundos.";
Gracias!
