Our attention spans are not very long maybe…

Our attention spans are not very long…maybe 20-40 minutes in front of a computer screen is all we can handle? We all are busy people, so sitting for two hours in front of a webinar can be daunting.
Also, web content should not be long and tedious. I learned in web design that paragraphs should be brief with lots of white spaces to rest the eyes.
Shouldn’t all this pertain to an online class as well?