max_execution_time php

//place this before any script you want to calculate time
$time_start = microtime(true); 

//sample script
for($i=0; $i<1000; $i++){
 //do anything
}

$time_end = microtime(true);
$execution_time = ($time_end - $time_start);
echo '<b>Total Execution Time:</b> '.$execution_time.' Seconds';

ini_set ( 'max_execution_time', 1200); //1200 is time in secondss