All VOD movies at the 501 channels have already been downloaded to the HDD in its entirety (not as a live stream, but as a download of files). This usually occurs in the wee hours of the morning, overnight IF you have your box in standby and are not using your DVR at those hours. That means the moment you confirm your purchase, it is immediately ready for viewing and trick play. In other words, it is just like when you have already recorded a show on your DVR that is in your list of recordings. You then have a 24 hour period from the moment you purchase to watch that VOD movie. The Channel 501 movies can also be accessed via Movies & More button when you press the DVR button once. It takes you to an interface that will even let you view the trailers for the movie before renting. Try it out.
Usually, only 1 movie at a time at channels 501 is 1080P. However, after some days or so, the movie featured in 1080P will change or rotate. For example, for several days the one 1080P movie is Star Trek. Then for the next several days it will be a different movie.
You may purchase a 1080P version of any movie, and if you TV can't handle 1080P 24, then it will automatically be converted so that it displays on your TV. For example, when you attempt to purchase a 1080P film, you will see a pop-up advising that there will be a short test to see if your TV can handle 1080P 24, if it can, great. If it can't then it will be converted to play on your TV. Be aware that some 1080P TV's may not be able to display 1080P 24. Your TV must be able to display 1080P 24 to view a Dish VOD in 1080P.
Now, DishONLine is a different service that requires a broadband internet connection. That content is downloaded via your broadband connection and includes HD movies and TV series. However, that service does require significant time to download and sufficient amount of program before allowing playback. HD will take a really long time. SD isn't too long a wait. Just approach it as kind of "Pre-buy" service--something like you have ordered it and when delivered you shall partake. Your 24 hour rental--for movies--begins the moment you initiate the PLAYBACK of the movie. So you can have a movie completely downloaded sitting for days, but the clock won't start ticking until you first begin to play it back.