Hey I figured it out me-self

Pizza store - opens at 11 AM, closes at 10 PM. So under zen_configuration, configuration_title = Enable Free Options Shipping - in my DB config_ID 754 - configuration_value = True if open, False if closed. Crontab contains:

45 9 * * 2-6 /home/site/www/pizza/[priv]/set_delivery True
5 21 * * 2-6 /home/site/www/pizza/[priv]/set_delivery False

So I can take a Delivery order starting 15 minutes before we open and up to 55 minutes before closing (ref movie Falling Down)

set_delivery:
echo "update zen_configuration set configuration_value = '$1' where configuration_id = 754;" | mysql -u zc --password=xxxxxx zc

So when conf_value = False then the "Delivery" option on the Check out page just isn't there.

Hope this might help someone.