This is a Web Module option managed in the Web Control Panel that can be activated when high demand is expected for online sales

Where they are in the Queue
How long we estimate they will need to wait
How the Production that they are looking to book is filling
When this information will be updated

Further through the queue this could look like this

The trigger for the Queue being activated is a threshold of hits to the booking site. This can be more or less conservative depending on expected requirements. In other words if you want a faster booking experience for those Web Patrons in the ticket purchase process less than 5 hits per second could activate the queue so that there are less people contending for tickets, but that will mean a likely longer queue for those waiting

The management of the Queue is dynamic so can be altered even during a high volume of visits to the site. So if you are caught out, you can modify things on the fly:

Below will also list All the Productions that are selling online, so you can indicate perhaps the one that si booking the most to indicate to the Patron sin the Queue how fast that Production is selling and how full it is:

Advertising can also be combined with the Queue, refreshed every 30 seconds: