I was wondering if there is a way to calculate average time spent by users from Cart add page to Checkout page, Meaning average time taken by users from Cart add page to Checkout process.
If you have separate event for Cart Addition and Cart Checkout, we can get the Time Taken between the same by tweaking implementation. Check out for options to capture the same using the link : Measuring Time Spent | Adobe SiteCatalyst | Attack Low Hanging Fruit .
If you can capture the time in Events, then Average Time can be calculated with Time Taken / Page Views of Cart Addition and Cart Checkout.
Not sure on the ready made options available in Reporting Interface.