Sensei Content Drip

For each lesson in a course, you can specify when learners will be able to access the lesson content, either as a fixed interval after the date they start the course, or on a specific date.
Whatever schedule you decide upon, you are in complete control of your students’ learning pace.
Key Features

Set your drip schedule based on a fixed date or an interval after the course start date.
You can manually override the drip schedule to give learners access to any lesson at any time.
Your learners get an email notification on days when new lessons will become available.
Customize the message displayed to users when a lesson is not yet available to them.
This extension also prevents the possibility that users will buy a course, download all the content, then ask for a refund, essentially getting the entire course for free.