Why do TV shows from iTunes take so much longer than netflix on apple tv?

This is nonsense. My issue is similar to the original question, but rather: why do some purchases take literally hours to download, while others start playing almost immediately? This makes it clear it has nothing to do with quality or connection speed, but rather with some other mysterious variable.

That will be due to your network. Netflix adapts to the connection where iTunes is at a fixed rate and higher quality. It also needs to load a portion before playback begins.

What is your current connection via speedtest.net? You will need at least 6mbps

Make sure DNS is on auto (settings - general - network)

Using Ethernet will help rule out wifi issues

4.5 is not enough to view instantly. No, Netflix is adapting to the connection and thus you are getting lower quality. You can also switch to SD if you wish to view lower resolution via iTunes. That 2.5 hours is an estimate. You may also be experiencing interference over wifi, each device will be impacted differently, which will cause such figures. Using ethernet will help rule that out. If you are using a 3rd party DNS that will also impact performance.

Content is playing back within 5 seconds on my system and for most.

You are likely experiencing interference on top of your limited speed, this will not impact all devices in the same way. iTunes is not available on Roku, most others are using adaptive streaming like Netflix

Best to troubleshoot

Try ethernet and/or get a network report by going to istumbler or similar. The report will show signal strength, noise, nearby networks.

You are also free to test on another network

I have exactly the same problem. My last network test was 35Mbps download speed, yet my video takes forever to play on ATV2 and 3. No problem on Netflix. I have an Airport Extreme ac. So I should be fine there. Very frustrating.

Internet speed is only one factor. As stated above, Netflix adapts to the connection where iTunes is at a fixed rate and higher quality. It also needs to load a portion before playback begins.

Did you verify DNS?

If on wifi try ethernet

To see a status of your network you can get a report by going to istumbler, netstumbler or similar. It will show signal strength, noise, nearby networks.

You could also test on another network

I have a slightly different problem. If I buy a movie using Apple TV movies (the Apple app not Netflix!) it will play straight away. If I rent one I get the same 3-4 hour wait described above. Why is this?

Not sure why there would be a difference. Are they both the same resolution? I would still troubleshoot the network to make sure and test at a different location

Makes no difference. I can swap between a purchased film and a rented film. Rented film always gives the delay. Purchased film plays almost immediately.

I get 1.5meg/second downloads on all other devices and can stream purchased movies without any lag to my Apple TV. So for me there is a "feature" in the rental code that isn't in the purchased code (or Netflix!)

I dont think that would be the case. Both play instantly on my system and for most. What troubleshooting have you done? Did you test elsewhere?

Nope, and that doesn't rule out a network issue. You still need to do proper troubleshooting.