Disable automatic maintenance
In the Maintenance Settings, disable http://ads.example.com/www/admin/account-settings-maintenance.php, disable Automatically perform maintenance during delivery if scheduled maintenance is not set up and enable maintenance as a cron task:
cd /etc/cron.d
echo '0 * * * * root /usr/local/bin/php -f /var/websites/ads.example.com/htdocs/openx-2.8.7/maintenance/maintenance.php' > openx-maintenance
chmod 644 openx-maintenance
touch /etc/crontab