Took awhile to download the update from the App Store (I don't know exactly how long because I went and did other stuff). The actual upgrade took about 25 minutes - I went and had lunch and it was done. The downloading, for me, was definitely the longest part.
Took me 16 min to download. And around 40 min to fully install. It said 35 min while it was installing, but then after the laptop restarted, it said it was finishing the installation and that took around 5 minutes. So almost 1 hour total, from starting the download from the App Store to being able to use Mavericks.