How to change start hour of day in iPhone Calendar app

Alex, thanks for you answer. However, if I am not mistaken, the instructions refer to Mac OS X Mavericks, not iPhone/iOS. Actually, I'd like to no know how do do the same thing in iPhone/iOS. I am happily using this functionality with my Mac BookPro and iMac and I'd like to be able to do it also with iPhone in iOS.

Thanks Meg, that's what I thought. Actually, I have Week Cal installed and it supports the configuration of the start hour of the day and I just wondered if I could do the same with Apple Calendar and on a Mac.

I'd just like to stick to Apple software as much as possible. I've been using Macs since 1989. When I was younger (and even more foolish), I used to have lots of third party software which worked often times well, but after upgrading the operating system all of them didn't work so well any more or didn't work at all. I learned the hard way to respect the KISS principle (Keep It Simple, Simpleton): the fewer software vendors I have the less I have trouble. Though, I must admit that with iOS I have had much less problems with third party software than I used to have or have with Mac.