If you would like to ensure that your learners always return to your site and receive fresh lessons, one way to proceed would be to set a Project Expiry Date.
Choose File > Publish Settings. From the Project category at the left, select Start and End. Then select Project Expiry Date.
Click the Calendar button at the right, select a future date and then click the OK button. Optionally, type a message into the available text field. Learners will see this message when they attempt to view the expired lesson.
Once you publish the lesson, the Project Expiry Date is embedded within the output files. Learners will be unable to disable the Project Expiry Date. Instead of seeing the lesson, learners will see the message you typed should they attempt to access an expired lesson.
The ability to add an expiration date to published lessons isn't a new feature in Captivate 6. In fact, the feature has been available for years. What's new in Captivate 6 is the inability to disable the Project Expiry Date. You read that correctly. You may find yourself unable to disable.
Allow me to explain...
Many people download and use the free 30-day Captivate trial that Adobe makes readily available on its website. If you use the trial version of Adobe Captivate 6, and visit the Start and End area of the Publish Preferences, you will notice that the Project Expiry Date option is selected. You will also notice that you cannot deselect the option. Any projects that you publish using the trial will basically self-destruct after 30 days, making the Expiry feature an often overlooked and potentially embarrassing byproduct of using the trial version of Captivate. Should you publish lessons during your 30-day trial, all of those lessons will expire. If you then deliver the published files to a client, you'll likely have some serious explaining to do a month later. Ouch!
The issue is easily resolved by opening the trial projects with the licensed version of Captivate and republishing them. (The Project Expiry Date is disabled by default if you are using the licensed version of the software.)