Within Teamwork Desk, it's possible to set tickets to automatically close after 72 hours of inactivity.

To enable this feature: 

Click on the Settings cog at the bottom left of Teamwork Desk, and select "Company."

Enable the option "Auto close old tickets. 

When selected, tickets that are in a waiting status, but have had no response from customers within 72 hours will be automatically closed.

For more information see: What are the company settings