I started my update to my 6 @12:59. An hour and twenty later, I thought my phone had bricked. Nothing but a black screen for a few minutes. Then the white apple logo appeared and all was well.
Same thIng on the iPad Air 2.
None of mine took more than 25 minutes, start of download to finish. One, my iPad Pro, was just ten minutes. . . but then it is hella fast.