The dashboard module "Maintenance" (Dashboard > System > Maintenance) offers the possibility to set the whole website or only the order process on maintenance (in case of a bug in the ticketing system for instance) and to display a message on the maintenance page.
The notification has a date plus start-end time and can therefore be planned in advance with planned maintenance or when there will be an update of the ticketing system.
Select the type "disable user accounts and integrated ticketing" if all ticketing functionalities have to be deactivated. In this case the website is still available and functions as usual, but when communicating with the ticketing system a message will appear (think of logging in, check-out, order history, etc).
For big updates on your website we usually set the queue of the website to 0. This means that the website is not available anymore. This can be handy for certain test steps before setting the website live again.
In this case you can also display a notification on the maintenance page. You can schedule a news items with type "notice in queue".
Good to know: the maintenance is active for all regular visitors. During maintenance the website will still be available for people having access to the dashboard. In the "Queueing" module there is the function "Bypass queue" which is used during maintenance to control the website.