我是亲眼见证的...这种事我每个LEVEL都在HNK看见 估计争取成功概率不大

I am not in Hong Kong test center. However, it is possible that the door was closed at 830am while the check-in process did not complete within 15 minutes.

In such circumstance, the start  the exam should be postponed until all the candidates in the test room have been successfully checked in. As long as the total duration is 3 hours, it is acceptable that the exam does not start from 9:00am exactly.