How long does it take to install iOS 8.1.3?

Probably 20-30 minutes. Download speed on your network is a factor.

Mine approximated time was 6 hours just now... now increased to 7 hours

I not so sure... my now my download time drop to 1hour... mine is from 8.1.2 to 8.1.3

How long do you think the update would take if you update from 6.1.3 to 8.1.3 (for iphone 5)?

I am going from 8.1.2 to 8.1.3 for an iPhone 5c through iTunes. Right now it is showing 18 hours, assuming the download does not fail. I am on my 9th attempt.

For my iPad 3 it was even worse. The best time I saw was 76 hours but I have given up on that update for a while.

There must be something very wrong with your phone and iPad or with the way you are doing the update. You say that you are on your 9th attempt to update your phone. That is very odd. And for your iPad to take 76 hours is also very odd. My updates on my iPhones and iPads each took about 20 to 30 minutes. I would suggest a trip to an Apple Store to have a genius assessment to see where the problem is.

Are you updating over the air on the device, or using iTunes on your computer? The over the air update is about 130 MB, so even on a slow connection it shouldn't be more than a few minutes. The iTunes update is 2 GB, so a high speed connection is essential. In addition, any antivirus that has real time file scanning enabled will slow it to a crawl, no matter how fast your Internet connection is. So disable your antivirus entirely, or at least turn off real time scanning before trying to update.

This is through iTunes. We have a 7Mb/s DSL line and doing various speed checks shows that it is within parameters. There is no anti-virus software on my iMac. My suspicion is this is something on CenturyLink's end (which they vehemently deny) since our previous iPhone 4's took huge amounts of time to update as did our original iPad.

I just keep trying.

On a 7 Mbps connection it should take about an hour. If it's really 7 Mbps. Have you measured it using, say, speedtest.net?

I have checked it through several test sites. Connection speed is running 6.5 to 7 Mb/s.

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