I kicked off the iOS 8 update on my iPhone 4S at 11:40 this morning. The download (all 940 GB of it) took a reasonable amount of time, given the network connectivity at work.
Then the installer spent roughly 45 minutes “preparing” the installation.
Although I’d originally pressed a “Download and Install” button, the installer then stopped completely, waiting for me to press an “Install” button.
Then the downloader spent several minutes (I didn’t get a good count, but it was around five) “verifying” the download.
After verification came the expected reboot and upgrade. It’s been 24 minutes so far, and the progress bar looks to be at about 60%.
I can understand Apple’s desire to be safe rather than sorry for this sort of operation, but a warning might be in order: This procedure will take well over an hour; please plan accordingly.