Not sure that turnout is over a million. Even HKFP are being cautious and only switched from “tens” to “hundreds” of thousands about an hour ago. I do hope that you are right though! And even 1 in 10 or 15 would be remarkable.
Edit: the SCMP has some turnout figures. As usual they vary wildly.¹
1. https://www.scmp.com/news/hong-kong/politics/article/3013725...