My experience is that, *after* the download, the hard drive is working 100% installing the bits and pieces within the game files.
So it does not seem to be a Steam issue, but more about a lot of pieces that are inserted within the game. I am not an expert though, but my SSD was running at 100% for a long while.
Took my computer about 45 minutes also.
At least I did not get the infamous reload the entire game issue.
