This allows you to set an expiration date for any custom question you have. 

For Example: If you only want to offer free T-Shirts to a certain date, you can now have the question set to automatically expire and close on the specified date and time.

You can set this up when you are creating or editing the custom question in the Custom Questions area under the Event Setup menu on the right. 

Just be sure to put in a date and time when setting up or editing the question: