Using the top 20 bestsellers on both the physical and Kindle bestseller lists, the average stay for a title on the lists is 155 days on Kindle and 196 days on the physical. The discrepancy between those numbers is inflated because of The Hunger Games books, which have had a considerably longer stay for physical than for Kindle. The physical list, on average, also seems to get more books that become bestsellers quickly and then recede, leading to one or two books per day that see a huge sales spike that Kindle books don't experience.