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Once you start watching your movie, you can view the rented movie as many times as you wish within the 24-hour (or 48-hour) window.
If you don't watch your rented movie, it will expire in 30 days and disappear from your iTunes library. You will need to rent it again in order to watch it.
That is correct.
You quoted it but I was going to correct your response by saying it is available for view as many times as you want within 24 hours of the first "viewing" (regardless of how much you watch, even a few seconds)...so technically it isn't really a "one time shot" as much as it's a "one day shot". This is something that I personally feel Apple could improve on, because the rental fee (to me anyways) is a bit much for a 24 hour limitation after it's started.