If all you need is the wall-clock time, rather than the CPU execution time, then it is simple to calculate:
//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);
//dividing with 60 will give the execution time in minutes otherwise seconds
$execution_time = ($time_end - $time_start)/60;
//execution time of the script
echo '<b>Total Execution Time:</b> '.$execution_time.' Mins';
// if you get weird results, use number_format((float) $execution_time, 10)
Note that this will include the time that PHP is sat waiting for external resources such as disks or databases, which is not used for max_execution_time
.