On a computer course, effectively no more than five hours.

That is assuming that the course has interesting content, is relevant to the learner, involves active learning, is broken into learning segments or chapters, and offers diversity in the subject matter.

In an ideal world, learners would step into the classroom with laser-like focus, and absorb hours of information without pause.

But the reality is attention spans waive and this is associated less with attitude and more with course duration.

Long courses routinely deliver poorer learning outcomes than shorter courses, but why?

It all comes down to science.

Selective sustained attention that is required in computer application learning, also known as focused attention, is the level of attention that produces consistent results on a task over time.

Common estimates of the attention span of adult learners range from 5 to 6 hours; however, there is no empirical evidence for this estimate. Wilson, Karen; Korn, James H. (5 June 2007). "Attention During Lectures: Beyond Ten Minutes". Teaching of Psychology. 34 (2): 85–89.

Practically, no human can really focus for 5 hours straight. People can choose repeatedly to re-focus on the same thing. Cornish, David; Dukette, Dianne (2009). The Essential 20: Twenty Components of an Excellent Health Care Team. Pittsburgh, PA: RoseDog Books. pp. 72–73. ISBN 978-1-4349-9555-1. OCLC 721335045.