How long does it take to install Windows 10?

I have just installed the Windows 10 from 8.1 today. It's actually quite a nice OS, up till now, I seem love it. The question is "How long does it take to install Windows 10?" I wonder this myself as I don't want to interrupt my work time. Here is my answer:

It depends much on your PC of course, real examples are here for you to figure it out:

My Lenovo U41 laptop (Core i3, 4GB RAM, Windows 8.1) took 1 hour to install from the time I clicked the GO button.

My friend's PC, however, took only 15 minutes (he is a designer with an core i5 processor and 8GB RAM PC from Windows 8.1).

Will update soon with my/my friends' PC status when getting green-light confirm from Microsoft.

James.
August 07 2015