Why would any intelligent person rent movies from iTunes? They're still the only one of the major digital rental services that limits every single rental to 24 hours once a movie has been started. Google, Sony, and Amazon all give you 48-72 hours for most rentals. Save me the Apple fanboy responses.
Well lets think this through logically. If you rent through iTunes, you can view it on your iPhone, iPad, Mac or Apple TV. Amazon, Google and Sony don't have apps for the Apple TV, so therefore you would have to download it to your iOS device via their app, then stream it to your Apple TV. That is an entirely additional step. Second, when I rent a movie, from whomever I rent it from, I usually finish that movie within 3-4 hours, let alone 24 hours. Who needs 48+ hours for a rented movie? Are you going to watch it 5 times?