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I updated my iPhone almost immediately yesterday, but had to wait until I got home for my iPad. It was impossible to do last night (slow, failed attempts), but worked fine today. I suspect either Apple's servers were slammed or if they have different content delivery networks, one particular set was slammed. When things are working normally, the download only takes a few minutes, and then a few more to install.
 
its prolly just the servers...I tried last night on my ipad and it said 50 hours...lol...I got up this morning and started it and was done in about 10 minutes...
 
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