Question

Whats the maximum execution time of cron. is it possible to modify it if so any side effects.

Answer 1

The accepted answer above is INCORRECT. Cron’s time limit in Drupal is hardcoded to 240 seconds. See the drupal_cron_run function in includes/common.inc, specifically these lines:

drupal_set_time_limit(240);

and

if (!lock_acquire('cron', 240.0)) {

(based on the source of Drupal 7.12)

So, there is no way to change this globally without hacking core. I have heard it suggested to call drupal_set_time_limit yourself inside of your hook_cron implementation, as doing so resets PHP’s counter. However that won’t help you when it’s a third-party module implementing hook_cron.