Your hours are renewed with each payment and shared between all profiles. This means that if you listen or read for two hours, and another profile for three hours, together you will have used up five hours.
Audio books
If you listen to an audiobook for one hour, one hour is deducted from that period. It works the same whether you are streaming or using the offline mode. It doesn't matter if you listen faster or slower than normal. Rewinding or jumping between sections does not count as time.
E-books
For e-books, a certain number of characters counts as one hour. This means that it doesn't matter how fast or slow you choose to read. Scrolling quickly or skipping between chapters also does not count as time.
If you read or listen to the same segment of a book more than once in the same period, time is only counted the first time.