You may receive a message such as “Maximum execution time of 30 seconds exceeded” or “Maximum execution time of 60 seconds exceeded”. This means that it is taking to longer for a process to complete and it is timing out. There are a number of ways to fix this error.
Method 1: Edit file wp-config.php:
Add the following to wp-config.php:
set_time_limit(300);
Method 2: Edit file .htaccess:
Make sure you back up .htaccess before you edit it.
Add the following to .htaccess:
php_value max_execution_time 300
Method 3: Editing php.ini
Add the following to php.ini:
max_execution_time = 300
See more: http://codex.wordpress.org/Common_WordPress_Errors#Maximum_execution_time_exceeded