The shopping cart is tied to the user's session. Sessions in Luminate Online can stay active indefinitely if a user is actively logged in browsing your site. For an inactive user however, they would be logged out after a period of inactivity as long as 20 minutes and as short as a few minutes. Session times vary based on the server load, so in times of high loads inactive users are logged off more quickly by shortening the amount of time they are allowed to be inactive. It is not possible to change a user's session time within Luminate Online, as this time is based on server availability at any given time. 

In summary, users can add an eCommerce item to their shopping cart, and it will stay there indefinitely until their session expires, or they log out.