I downloaded the Sierra installer at 1:30pm today (Before it was even on the "Front" page of the App Store). I noticed today while installing it is says that it should take "6 Minutes" to install, but it's been... I dunno, longer than 20 by now. It still says About 4 minutes remaining. The progress bar marches forward in chunks. Maybe it's because I'm using a MicroSDHC Card (40mb/s) in the Apple Card Reader slot through an adapter.
I dunno - Anyone else have thoughts on this?