Started unlocking roughly at 00:05 China time. Download size is like 0 MB but HD is working @ 10.5 MB/s to do something... it adds 500 MB to the game size. It's 00:12 and still working, seems half way. Will edit to let you know how long it takes (with an i7-4770 @ 3.40 ghz processor and a Samsung EVO 250 GB SSD).
EDIT: it seems steam first checks the pre-load (only HD working for like 20 mins) and now is downloading the 500 MB. So now 5 mins left to download (my internet speed is 1.4 MB/s)
TLDR: 20 mins to unlock pre-load and download with above specs.
ENJOY ALL and thanks for this months of hard waiting!
Will be back after the weekend for first games comments. Ciao