Although the overall pre-open session will last the usual time between 9 AM to 9:15 AM, the way orders are collected, prioritized and matched, will change starting today.
Here are the changes that stock market participants need to know:
As per the new framework, market and limit orders will be allowed between 9 AM to 9:05 AM, which is similar to the older rules.
However, between 9:05 AM and 9:10 AM, while the older rules allowed an extended general order entry window until 9:08 AM, the new framework only allows limit orders. No market orders can be placed, modified or cancelled during this period.
The random system closure used to take place between 9:07 AM and 9:08 AM under the old mechanism, which will now take place between 9:08 AM and 9:10 AM for limit order entries.
Under the new framework, market orders will get priority over limit orders during the price determination period.
What Do The New Pre-Open Rules Mean For Traders?
Traders who rely on the At-the-Market (ATM) orders to trade the overnight news or global gaps must act within the first five minutes, between 9 AM to 9:05 AM, as after 9:05 AM, market orders cannot be placed, modified or cancelled.
The previous rules allowed large institutional or retail traders to place big fake market orders near the end of the order window to drive prices up or down at the end of the order window at around 9:07 AM, only to cancel them before matching. With market orders getting locked at 9:05 AM, late-stage manipulation can be prevented, thereby ensuring a better opening price discovery.
As market orders will now get priority over limit orders during the matching process, traders who want guaranteed execution need to place them within the first five minutes. Limit orders placed between 9:05 AM to 9:10 AM will provide the liquidity backdrop to absorb these market orders.
The price-sensitive traders can use the 9:05 AM to 9:10 AM window to react to the initial order flow, without market orders creating a sudden price swing in the equilibrium price. This will mirror the CAS mechanism, thereby stabilizing the price discovery.