Well thinking about it, it asks you to shut down all running apps. But it still has to finish shutting down all your services and everything else. Not to mention save your profile along with any changes made.
Then restart.
Depending on when the script pops up with the results it also have to account for you typing in your password. Then possibly loading when you have set to load at boot.
So really it isnt a script to see how long you reboot. It is a script to see how long it takes to get from a workign desktop to a working desktop. Cause the only part that is truly the boot, is going from the BIOS to the login screen. Anything before or after that, is not part of the boot. It is part of Windows and can be highly affected by so many variables that are out of our control.