Within Teamwork Desk, you can set tickets to automatically close after 72 hours of inactivity.
Enabling auto closing
Click your profile icon in the top right corner of your site, and select Settings from the dropdown menu.
In the Settings area, go to the General tab and select the Site Settings subsection from the left sidebar.
Under General Settings, you will see an option to Auto close old tickets.
When enabled, tickets that are in a waiting on customer status, but have had no response from customers within 72 hours, will be automatically closed.
For more information, see: Understanding Ticket Statuses