Too short
For me, it's not about fairness but convenience for the customer. My wife and I frequently rent movies from DirecTV, and store them on our DVR so that we can watch them over 2-3 nights (I believe DirecTV deletes the movie from our DVR after 30 days). We have kids that go to bed around 8:30, so we find it difficult to watch a movie in one sitting. This has also been a problem for me when watching movies while flying. I watch most of a movie on the outbound flight, but can't watch the rest 1-2 days later on the return flight. If this policy is designed to force people to rent a movie more than once, it's customer-unfriendly to say the least.