I found vote4.hk a wonderful resource for understanding and simulating the Hong Kong District Council elections currently underway.
The turnout at every hour after polling stations opened (at 0730 HKT) is released within an hour. The best official place to get these turnouts is the government’s elections website, here: https://www.elections.gov.hk/dc2019/eng/turnout.html, and with the 2015 turnouts here: https://www.elections.gov.hk/dc2015/eng/turnout.html
The overall turnouts are so far as follows, with 2015 turnouts in brackets:
0730: 0% (opening!)
0830: 3.82% (1.28%)
0930: 10.41% (3.85%)
1030: 17.43% (6.79%)
1130: 24.37% (10.89%)
1230: 30.98% (14.48%)
For reference, the final turnout for the last District Council elections in 2015 was 47.01%, according to the 2015 turnout page.
Their ugly turnout graph makes the large change in turnout very clear: