Business texts and technical books are very different. I read math/science/programming books as well - I'm currently working through
Probability Theory: The Logic of Science by E.T. Jaynes. There's no way I could grok that book in 20 minutes.
10-20 minutes won't cut it for deep technical material, particularly if the book is designed to teach via working through examples. If you're reading a workbook, then take the time to work through the examples. Choose your workbooks carefully, since they require a more significant time investment.
Most non-fiction books, however, are written around a few simple, straightforward concepts - you can identify them in a few minutes. A few more minutes identifying examples, relationships to other concepts, and counter-examples / edge cases, and you've extracted 90% of the value of the text.
Almost every non-fiction book fits this model. It pays to tailor your reading approach to what you're reading.
As to value - in general, most business books are marginally valuable in isolation. Once you read many of them, however, very useful patterns begin to emerge. Recognizing and using those patterns provides the value.