The "limited time" to view a purchased PPV is really dependent upon what part of the day your purchased that movie. The earlier in the day you purchased it, the more time you have. PPV's are available something like 5AM to 2AM or thereabouts.
However, the ON DEMAND movies only give you a bit more time: a full 24 HOURS once you star to view it for the very first time. Then it is timed out and no longer can be viewed, but ON Demand is more expensive than movies via PPV.
I think part of the problem isn't that Dish is obscuring anything, but that MOST people know how the PPV systems on cable and sat work after over a decade of ubiquitous existence and Dish may have felt that a large print warning how PPV works was unnecessary. I have to be honest and say that I am really quite surprised that anyone who has pay TV doesn't know the legacy model of how a PPV movie (not a boxiing match, etc. which is a PRE-purchase) works.
However, I don't think it is your fault as there will be people who still may not know, but it's a lot like coming across an adult who doesn't understand that hotels, as a rule, have 12 noon check out time (this is often NEVER explained in person and finding the info is in TINY itty bitty writing lost among the paperwork, etc. or that the Hotel is not going to give you a discount because you checked in at 10PM instead of the usual 3PM first opportunity for check-in or that a hotel bills you for all your telephone calls made on their phone in your room (phone charges have to be in small writing somewhere, but we just don't look for it. Hotel staff never tell you upon your request that they launder your clothes that there is a charge for it; or that when they ask for your room number it is only to confirm you are a guest but that it means it will be billed for the service; they believe you surely must know how it all works (OK, I am asking for your room number so I may charge this to your bill at check out. Do you understand and abide by this disclosure), and won't try to have the charge removed because you didn't know about it. How hotels "work" (just one example) and its practices my be lost on teen-agers with little life experience, but we expect more from a grown adult. Consider this a learning experience and now you are ahead of the game.