There are many variables here. The most important being your connection speed. With a Wi-Fi connection at the U.S. average (about 25mbps) the process should go as follows (assuming you are updating from the latest version of iOS 6):
Download time: 30-45mins
Installation preparation time: 15-20mins
Installation (first loading screen): 15-20mins
Installation (second loading screen): 3-5mins
Final set-up: However long it takes you to type your Apple ID and password
It was realeased for download on September 18th, 2013.
There is no way to undo iOS 7 after restoring your iPod because iOS 7 is not released yet. However, to downgrade the iOS of your iPod simply download the firmware of the iOS you want from the Internet. While in iTunes, hold shift as you click "Restore my iPod to factory settings" and choose the file you just downloaded and your iPod should be on a lower iOS.
No, you cannot. Even if you are able to, you would encounter a number of hardware compatibility issues.
Yes you do. You will also need iOS 7 to download onto the device.
7 months
Ios 7 is the latest ios. Ios 7 is available on the fifth generation iPods, recent iPads and iPhones 4 and 5.
No it did not. It had IOS 6. But you can get IOS 7 on it. Also when IOS 7 came out they put it on the iPod 5 in stores.
Very long...
It depends on your internet speed. The file is around 2GB.
Yes, you can run iOS 7 on the iPhone 4.
There is no way to downgrade from iOS 7 without disobeying the Terms.
Yes, we are up to iOS 7 beta 4 so far and this beta is available to iOS developers.