Hello, this is Director Shirokuma. 🐻❄️
I learned that US stock exchanges are planning to expand trading hours to “23 hours a day, 5 days a week” starting December 6, 2026. As someone who builds automated trading systems for US stocks while living in Japan, this is news that catches my attention.
What caught my interest isn’t just “whether we’ll be able to buy at night.” If stock prices move during the US night, won’t the way price movements appear at the start of regular trading and the performance of trading rules change as well? For example, will the “gap” where the next day’s opening price jumps significantly from the previous day’s closing price become smaller? This time, I will consider the impact on automated trading based on this question.
December 6: What is scheduled to change?
Nasdaq and NYSE Arca are not planning to make regular trading hours 23 hours long. Regular trading will remain as it has been, from 9:30 AM to 4:00 PM Eastern Time. The plan is to make the previously empty 9:00 PM to 4:00 AM slot the new overnight trading period out of the extended hours surrounding the regular session.
If it connects with existing time slots, it will form a shape where you can trade almost continuously for 5 days a week, from 9:00 PM Eastern Time to 8:00 PM the following day. It is not “24 hours, 7 days a week” where you can trade on weekends. Japan time is an estimate converted based on winter time, and it will be one hour earlier during US daylight saving time.
However, December 6 is the currently scheduled start date. This is contingent on preparations such as market data distribution and necessary approvals. Also, it does not mean that all US exchanges, all stocks, and all brokerage accounts will support it in the same way from that day. Nasdaq Official FAQ / NYSE Arca Official FAQ
“Buying US stocks at night” is not a first
This is a slightly complicated part. Webull Securities, which the laboratory uses, already offers 24-hour trading including overnight hours for some US stocks and ETFs. The target is about 900 stocks designated by the company, and what you can choose at night are limit orders. Webull Securities 24-hour trading guide
In other words, this story is not about “being able to trade at night from Japan for the first time on December 6.” It is about exchanges like Nasdaq and NYSE Arca expanding their overnight trading hours.
Since there is already overnight trading, it cannot be said that “stock price movements will definitely change if exchange hours are extended.” How the orders participating at night and the way prices are set will change is a research hypothesis to be verified with data after the start.
Furthermore, being able to trade at night on your own screen and being able to place orders for the same stocks and time slots from a self-made program are different things. Webull Securities’ OpenAPI provides information on US stock order and market data functions, but how this exchange expansion will be reflected in Japanese accounts, target stocks, and API order conditions needs to be confirmed before the start.
How will price movements change with overnight trading?
Even if overnight trading on exchanges begins, it does not necessarily mean that price movements will change. At the laboratory, we are looking at the following three points as hypotheses to verify after the start.
① We might be able to see the “middle” of a gap
Gaps are the difference between the closing price of the previous day’s regular trading and the opening price of the next day. If prices are set at night, we can track how the price moved during that time. The difference between the latest overnight price and the opening price might become smaller, but it does not necessarily mean that the conventional gap itself will shrink.
② The time of surges and pullbacks might change
The market might react to news such as earnings from the night, and the rise and pullback might complete before regular trading begins. In trading rules that only look at the opening price, there is a possibility of overlooking the middle of that process.
③ Prices might be prone to jumping during times with low trading volume
If there is little overnight trading, the last price set by a small number of trades could move significantly, and the spread between the buy and sell prices could widen. If you treat that price as a “price you can buy at during regular trading,” you will overestimate the results of your trading tests. SEC After-Hours Trading Guide
Where should we review our trading rules?
The laboratory is currently aiming for short-term swing trading of US stocks. Even if you do not place orders at night, nighttime price movements may change your trading decisions or order prices at the start of regular trading hours. Therefore, we will consider the impact and countermeasures as a set.
Attention must also be paid to record-keeping. According to guidance from Nasdaq and NYSE Arca, trading between 9:00 PM and midnight Eastern Time is scheduled to be treated as the next calendar day. If you include nighttime data in your verification, do not summarize it only by the Japanese date; ensure you can identify which trading day and time zone the price movement belongs to. Nasdaq Official FAQ / NYSE Arca Official FAQ
Will this be a tailwind for the market as a whole?
As the director, I am also hopeful that it will become easier for investors in Asia and elsewhere to participate during their own daytime hours, bringing new capital into the US market and potentially boosting the market as a whole. Nasdaq also cites easier access to US stocks for global investors as a goal of this expansion. Nasdaq 23-Hour Trading Guide
However, even if trading volume increases, it does not necessarily mean that only buying will increase, and we cannot say that stock prices will rise solely due to the extension of trading hours. After the launch, I would like to observe nighttime volume and its impact on regular trading, separating expectations from actual changes.
Will the laboratory immediately expand to nighttime trading?
At the moment, we have no intention of expanding into nighttime trading. This is because there is no need to move our short-term swing trading rules to nighttime just because the hours have been extended.
However, not engaging in nighttime trading is different from ignoring nighttime price movements. Once the new trading hours begin, we will observe gaps, nighttime surges/reversals, and price jumps by time zone. We will compare them using the same definitions before and after the start, and consider whether we need to adjust the prices we check before ordering or the conditions under which we skip orders. Since price movements also change depending on factors like the presence of earnings announcements, we will not judge that “23-hour trading is the cause” based on just a few days of data.
Even if we do not plan to trade at night, we will incorporate the impact of extended nighttime trading on our daytime trading rules into our systems and verification. That is how the laboratory views 23-hour trading. 🐻❄️
※ This article summarizes planned market changes and the laboratory’s considerations based on official announcements as of October 19, 2026. Start dates and usage conditions are subject to change. This does not constitute investment advice or an indication of future profits.
