I want to update my iPhone
How long will it take for back up my iPhone through Mac?
iPad 2, iOS 6, New update
My iPhone 6 takes only a few minutes to backup to iTunes on a fairly new Mac that has USB 3 and a Fusion Drive. It may take a bit longer if your Mac is older or you iPhone has more storeage than mine.
However, the backup is the quick part. The actual upgrade can take quite a long time depending on how fast your internet connection is for the initial download. I typically assume that it's going to take an hour from when I click the button to start the update.