Open Seats
Game creators can add Open Seats to their game in the place of a player. Any game with open seats is considered an Open Game. All open games are listed on the Open Games Tab, which is located under the main Multi-Player tab.
Open seats are a great way to meet new players or for getting a new game up-and-running quickly.
To make an open game, just use the "Add Open Seat" button on the last step of the create game wizard.
Expiration
In the event that an open seat is not filled after too long, it will expire and will no longer be advertised on the Open Games tab. This is a safety mechanism designed to prevent undesirable games from clogging up this area for long periods of time.
Open seats in real-time games expire after 1 hour, and open seats in multi-day games expire after 12 hours. The host can reset this timer simply by pressing "Change Players" and then "Confirm".