The expiry type allows you to choose how long you want your order to be in the market.
The order is open (in market) for the day the order was placed and will expire once the market has closed for trading on that day.
Good Until Date
Good until date allows the order to remain open (in market) until the predetermined date, which gives you more opportunities of the order being filled. If the order is not filled before the predetermined date the order will be cancelled.
You can choose an expiry date for a period of up to 6 months from the date of the order placement.
When trading US or Hong Kong securities, you will only be able to place day only orders.