No orders can be submitted between 9:29 – 9:30, as this is the preparation period for market opening of the exchange.

One lot is the smallest trading unit of Hong Kong stocks.
In the Hong Kong stock market, the number of shares per lot is different, one lot may be 100 shares, 500 shares, 1000 shares and 2000 shares. For example, 700.HK Tencent Holdings is 

Hong Kong stocks are settled in T+2, which means securities companies and CCASS will be cleared on the second working day, and the funds and stock will be settled by then

Share Split/Merge
Example of share split: Tencent Holdings Ltd (700.HK) had possessed a 1 into 5 share split on 15 May, 2014.
The value of the shares held by the shareholders in the process of the share split remains unchanged, but the number of shares will change. In the process of share split, there may be a temporary stock code, but it will be restored to just one stock code in the end.
Share merge is the reverse process of share split, i.e. certain number of shares will be merged in to one.
 

Allotment
Allotment is the placement of shares by the listed company to the shareholders.
After the clearing on the day before ex-date, a client may take part in the allotment if he/she is 
a shareholder of the listed company.
Allotment refers to the process that shareholders may earn a right to buy certain number of new shares 
by owning existing shares. The right will be allotted on the payable day after the market is closed.

Bonus Shares
Bonus shares is also referred to bonus issue.
After the clearing on the day before ex-date, a client will be given bonus shares if he/she is a shareholder 
of the listed company.
The bonus shares will be transferred to the client's account on the payable day.

Dividend/Special dividend
Dividend refers to the issuance of interest to the shareholders, i.e. cash.
After the clearing on the day before ex-date, a client will take part in the dividend issuance if he/she is 
a shareholder of the listed company.
The dividend will be transferred to the client's account on the payable day.
Special dividend is a kind of dividend, but for a special reason. For example, a listed company earned a 
lot in an investment, but that is not part of the main business, so the listed company would issue special 
dividend.

The Volatility Control Mechanism (VCM), also known as “cooling-off period”, in the securities market was launched on 22 August 2016 by the Hong Kong Exchange, in order to safeguard market integrity from extreme price volatility arising from trading incidents such as “Flash Crash” and algorithm errors.
VCM triggered if a stock is ± 10% away from the last traded price 5-min ago; 5-min cooling-off period will start to allow trading within the band only; normal trading will resume afterwards. This applies to key HSI & HSCEI constituent stocks (81 stocks).

Yes.  Hong Kong stocks trading is T + 0