Thanks for using Bitnami. Could you please let us know why you need to increase this value? Did you get any error? I see that you edited the php.ini file and set the max_execution_time to 300, but I also see that you edited the apps/wordpress/conf/htaccess.conf file and included this block
php_value max_execution_time XXXX
You literally used XXXX and that's not a valid value. Apart from that, you included this change inside the Akismet's configuration so it won't be available for the rest of WordPress' pages and plugins.
So please remove those lines from the htaccess.conf file, restart all the services (
sudo /opt/bitnami/ctlscript.sh restart) and let us know more info about what you are trying to achieve so we can provide better help.