At-Auction Limit Orders are very similar to At-Auction Orders, but an at-auction limit order is an order with a specified price. They are available in Pre-opening Session and Closing Auction Session.
Pre-opening Session
【Input Period】          Pre-opening Session   9:00am - 9:15am
【Matching Period】   Pre-opening Session   9:20am - 9:28am
【Note】
1.All at-auction limit orders cannot be changed or canceled after 9:15am.
2.At-auction limit orders are matched in order.
3.Any outstanding at-auction limit orders at the end of the Pre-opening Session will be carried forward to the Continuous Trading Session 

Closing Auction Session
【Input Period】             16:01 - 16:08   ( 16:08 - 16:10 is the Random Closing Period ) 
 16:08 - 16:10
【Matching Period】      16:08 - 16:10
【Note】Instructions and precaution
1.At-auction limit orders cannot be canceled after 4:06pm.
2.At-auction limit orders are matched in order.
3.Another 30% of the assets will be frozen by the system after the At-auction orders, the assets will be return automatically after the order be traded or cancelled. 
4.In the afternoon Continuous Trading Session, the outstanding bid orders (The trading object is limited to Hang Seng Index constituent stocks and the bid price must meet the closing price limit) and sell (Hang Seng Index constituent stocks, State - owned constituent stocks, AH stocks, and the sell price must meet the closing price limit) orders will be automatically transferred to the Closing Auction Session.

At-auction orders will be cancelled after Random Closing Period if it is not matched.

Ordinary trading, that is enhanced limit order, which you could buy / sell at the specified price.

【Input order Time】      Client can input advance orders after the market close, the order will 
be automatically submitted to the HKEx by CNI Securities Trading System on 
the next day at 9:00 am.
【Matching Period】     Trading hours : 9:30am to 12:00pm  and   1:00pm to 4:00pm
【Note】
1.If the stock does not meet or exceed the limit price, the order will not be executed, and any outstanding limit order will be automatically cancelled after the day of closing.
2.Enhanced limit orders can be matched with up to 10 waiting groups at the same time (which can be bought or sold at a better price).
3.The selling price shall not be lower than the best bid price of 10 price units, not higher than the best selling price of 24 price units (the price unit of each stock depends on its share price).
4.The bid price should not be higher than the best selling price of 10 price units, not less than the best bid price of 24 price units (the price unit of each stock depends on its share price).
5.Part of the matched enhanced limit orders can be cancelled or changed, but only for the unmatched parts.
6.In the process of changing orders or cancelling orders, the original orders are still in effect, so it might be failed to change or cancel.
7.If the bid price of the order is higher than the market price or the selling price is lower than the market price, the order will be matched at the best market price (ie market price).