What is the Global Expiration Timer?
This timer shows when all Event Buildings of this type will expire. They will be removed from all bases and no longer be claimable from the inventory, regardless of when they were obtained or placed. Only some Event Buildings have Global Expiration Timers, while others will last a set time. (Typically 7 days.)

What happens when I destroy an Event Building?
You can now destroy Event Buildings on your base, allowing you to place a new Event Building without having to wait for your old one to expire.

To destroy an Event Building, you first have to tap on that building. Then, tapping on the Destroy (trash can) Button will let you permanently delete the selected building, so be sure you’re ready to see this one go. You can also replace your old Event Building by claiming a new Event Building from your inventory.

A destroyed Event Building is permanently lost and not returned to your inventory.