Course Structure: Time or Talent?

If the Shinkansen were used as the standard of measure for
time spent on track, the course would be worth less credits
than if a slower train were used.

In Tony Bates' Nine Steps to Quality Online Learning, he discusses using time spent on the course as a measure to help structure a course.  While I see the logic behind this, I couldn't help but wonder if we need to re-think this model of credits based on average time spent in the course.

In the days of rote memorization and regurgitation, time on task often was a good indicator for performance.  However, in today's learning environment where we focus more on understanding and critical thinking, time on task doesn't always correlate to performance.  In fact, some students who spend long hours on task still may not grasp a strong understanding of concepts and others, who spend little time, may.  How, if at all, could we correlate credit hours to understanding rather than time spent on task?