In Codeignitor version 3.0.x the system/core/Codeigniter.php do not contain the time constraint as well as inserting
ini_set('MAX_EXECUTION_TIME', -1);
will not work since codeignitor will override that with its own function set_time_limit() . So either you have to delete that function from codeignitor or simply you can insert
set_time_limit('1000');
in the beginning of the php file if you wanna change that to 1000 seconds. Set the time to 0 (zero) if you want to run it as long as it want.