configuration variable puts a default value of 30 seconds on how long a script may run before timing out. If you have access to php.ini, you can change it there. If not you can set it in the .htaccess file for your dokuwiki installation:
php_value max_execution_time 45
, where it says:
You will need "AllowOverride Options" or "AllowOverride All" privileges to do so.
If you don't have these privileges, contact your server administrator.