It has been a few months since I worked with my free Pandora account, but my cutoff was at eight hours. Sometime prior to cutoff, however, they would stray off or repeat the program -- probably to see if I was paying attention. If I did not immediately give the stray track a thumbs down, I would be punished later (for falling asleep at the screen) because the stray genre would be permanently added to the program. I suspect (without proof) that these stray tracks were cheaper than the others.