Here are some links about this problem. Forget the links, apparently you must have 10 posts before you can include links.
It is unclear to me whether the problem is caused by Verizon FiOS, or by Apple's new CDN (content distribution network).
One of the fixes that has worked is to change the DNS server that you use. This page has a list of alternative DNS server iPs. Again I'm not qualified to post links, but you can Google it.
I changed the DNS servers in the Actiontec Router. The sign in info is on the label. Go to Main, My Network, Network Connections, click Edit on Broadband Connection, then Settings. Change DNS Server from Automatic to Use the following ... and enter the IP address from the link above.
I first tried Google, then Level3, then OpenDNS Home. The first two had no effect, but with the third, instead of indicating that the download would take 34 hours, it said 8 minutes which turned out to be accurate. I now have iOS 8 on my iPad. Apparently, it is somewhat random which DNS server will work, and some have reported that while one DNS server worked well for one download, it did not work so well later. This has happened to me. When I try to download the iOS update for my iPhone, I am back to (now) a 62 hour estimated download time. I will probably try some more different DNS servers to see if I can get it done, or else just give up and go somewhere tomorrow where Verizon FiOS is not the Internet provider.
Others in the thread above mentioned using a VPN, but I don' have one.
I don't understand why this problem is not in the news, as there must be many, many people with the same problem. I would have thought that iMore would be on top of this as you have been very good with other iOS 8 issues.