Upon launch, the user will be notified that they have a certain time-frame to complete the course.They can close the course and come back to it, but access to it will expire within that certain time (a few days or weeks).
We’re planning to build this into the next version of our new Content Drip extension – http://www.woothemes.com/products/sensei-content-drip/
One alternative way to do this would be using Groups as described in this post – http://www.woothemes.com/2014/02/creating-a-tiered-membership-site-with-sensei-and-groups/
When you create a product that grants access to a Group, it allows you to set a duration, after which the user will be removed from that group.
Have you considered a free WordPress plugin that lets you expire a User's login?
Cláudio Luiz commented
This would be great. Currently too easy to share logins with no deadline esp on a subscription
Is there a way to restrict a student to progress to the next lesson if they have not spent adequate time on the current lesson?
I have plans to do this and think I have solved it: Combine it with WooCommerce Subscriptions plugin
Urs Frei commented
If not possible within Sensei I would try to solve this via an integrated mailresponder to manage the timing.