Well what is your internet speed? I've got 40mbps download speed, and as far as I remember, it took roughly an hour to download, definitely no more than 2 hours. Your internet speed will obviously be a big factor in how long the download takes.
I didn't calculate my time, but i would estimate about 3 hours so far it's been downloading. I have 10mbit connection and launcher is showing 1.44MB/s. Some point it showes 29GB remaining, now it's 2.8GB, so it's like going through different pack files or something bizarre. It has progressed 21%. Really weird considering this is not a fresh install. I used to play long time ago back before Windows 10 came out so base game should already be downloaded. At least i can see the numbers moving so i'll leave it crunching for the night...