Cron jobs terminate prematurely on amazon ec2 cron

Question

I am using amazon ec2 server and I have set up some cron jobs on crontab.

Sample for setting up cron job

58 11 12 * * php /var/www/html/folder/index.php controller/function/parameter

When I try

crontab -l

on putty they all appear and everything seems to be working fine.

But cron jobs with lengthy execution time tend to stop prematurely without generating any error in log file.

I am also setting the large execution time at the top of my php script

ini_set('max_execution_time', 600000);

I couldn't figure out whats happening. Any kind of help will be appreciated.