Earlier quoted context omitted.
If you include the value of your time, the library is a more costly option to acquire a book than Amazon for many affluent readers. And most libraries have a small fraction of the books one might want. The fact that people are choosing an efficient way to get the books they want is hardly evidence of inelastic demand.
You're saying that time is valuable. The cost of the book is the dollar price + the time to acquire + the time to read it. You're saying that the middle cost is significant. That suggests that the latter cost is also significant. Therefore lowering the dollar price of the book has little effect on the total in the above equation.
Even if we agree that the total cost (including time) of acquiring and reading a book is high, that does not indicate that demand is inelastic.