Your server has default Maximum execution time set to 30 seconds. You need to modify it.
Method A: via php.ini
The path of php.ini is varied as per server environment. For example,
- XAMPP:
- C:\xampp\php\php.ini
- XAMPP control panel > Apache Config > php.ini

- WAMP
- C:\wamp\bin\apache\apache2.4.9\bin\php.ini
- Right-click on WAMP shell icon (near watch) > PHP > php.ini
- cPanel:
- /home/username/public_html/php.ini
- cPanel > Software > MultiPHP INI Editor

- Other: Just google with OS or Panel to find the path of php.ini
Now, Add or Edit php.ini and search for line max_execution_time and replace line or value as below,
max_execution_time = 300
Remember, here 300 means 300 seconds (~5 minutes). If you still encounter the error then increase this value and retry.
Method B: via .htaccess for Apache server
Locate or create the .htaccess file at the root or home directory. Such as public_html. Add or replace the line as below
<IfModule mod_php5.c>
php_value max_execution_time 300
</IfModule>
Method C: via wp-config.php for WordPress website
Locate the folder where WordPress installed, you can see the wp-config.php file there. Search and add or replace below the line,
set_time_limit(300);
So these are the most common method to control execution time. Hope this will helpful to you. In case, other method work then kindly share them.