From an Era of Watching 'Yesterday's US' to 'Today's US': How Will 23-Hour US Stock Trading Change Japanese Stock Day Trading? [n+Market]
Starting December 6, 2026, 23-hour weekday trading is scheduled to begin in the US stock market.
Looking only at the news,
it seems like a story about
“being able to buy US stocks during the day in Japan.”
That is certainly a major change.
However, for those of us who primarily trade Japanese stocks, I don’t think that is what is truly important.
What I believe is the biggest change is
shifting from an “era of watching yesterday’s US market” to an “era of watching the US market as it moves right now.”
This is it.
■ Until now, Japanese stocks have used “last night’s America” as material
Let’s consider the Japanese stock market up until now.
For example, last night,
NVIDIA was up 5%.
NASDAQ also rose.
The SOX index also saw a significant gain.
Then, in the Tokyo market the next morning,
“Today is for semiconductors”
becomes the sentiment.
Advantest, Tokyo Electron, Lasertec, SCREEN,
and others are bought all at once.
Conversely, if NVIDIA falls sharply, semiconductor stocks will be sold off in unison the next morning.
In other words, the Japanese market was
a market that would fully price in the previous night’s US results all at once the next morning
as well.
How did US stocks perform?
What happened with the exchange rate?
How was the NASDAQ?
How was the SOX index?
Checking this in the morning,
‘So, how will Japanese stocks perform today?’
is what one would think.
For those trading Japanese stocks, this has been a familiar scene for many years.
■ However, this will change starting in December
When US stocks become available for 23-hour trading, US stocks themselves will move during Japanese daytime hours.
In other words, while the Tokyo market is open,
NVIDIA will also move.
Micron will also move.
Microsoft will also move.
Amazon will also move.
Alphabet and Meta will also move.
This is a very big deal.
Until now,
NVIDIA was up 5% last night
—we were trading Advantest using that past information as a basis.
From now on,
Is NVIDIA up 5% right now?
Has it dropped to up 3%?
Is it rising further to up 7%?
We will be trading Japanese stocks while watching that in real time.
■ ‘It was up 5% yesterday’ will no longer be enough
For example, at 9:00 AM.
NVIDIA closed up 5% last night.
Based on that,
let’s say Advantest starts up 4%.
Until now,
‘That makes sense because NVIDIA was up 5%’
was fine.
However, it will be different after 23-hour trading begins.
At 11:00 AM Japan time,
NVIDIA
up 5%
↓
up 3%
↓
up 1%
has dropped.
If that happens,
the information that
‘NVIDIA was up 5% last night’ is already old news.
What the market will look at is
‘what NVIDIA is doing right now’
.
Then, Advantest might also
+4%
↓
+2%
↓
+0.5%
and move in tandem.
The reverse is also true.
If NVIDIA rises further during Japanese market hours, Japanese semiconductor stocks will also be bought additionally.
In other words,
it is not last night’s results, but current US stocks that will move Japanese stocks.
There is a possibility that the market will become like that.
■ The biggest factor is ‘US corporate earnings’
I am paying particular attention to this.
NVIDIA.
Micron.
AMD.
Broadcom.
Microsoft.
Amazon.
Alphabet.
Meta.
The earnings of these companies have had a very significant impact on Japanese stocks until now.
However, from now on, the way that impact manifests will change.
■ Earnings announcement → Japanese stocks react in real time
For example, suppose NVIDIA announces strong earnings.
Greatly exceeding market expectations,
NVIDIA +8%.
Naturally,
Advantest
Tokyo Electron
Lasertec
and others will also see buying.
However, during the subsequent earnings call,
‘Profit margins will decline next fiscal year’
‘Demand for China is weak’
and other such remarks are made.
Then NVIDIA,
+8%
↓
+6%
↓
+3%
↓
+1%
rapidly shrinks its gains.
Then, selling will emerge in Japanese stocks as well.
In other words, during Japanese market hours,
the price movements surrounding the earnings of US companies will be directly reflected.
This is a significant change.
■ ‘A CEO’s Remark’ is Scarier Than Earnings Figures
Especially in the AI market,
it is not just the earnings revenue and profit that matter,
but what the CEO says
is extremely important.
For example, if Microsoft says,
‘We will further expand capital investment for AI,’
then,
Microsoft
→
NVIDIA
→
Broadcom
→
semiconductor manufacturing equipment
→
data center-related
→
power cables and optical communications
funds may move in that sequence.
Conversely,
‘We will take a cautious look at the profitability of AI investments’
‘We will slow down the pace of capital expenditure increases’
would trigger the opposite movement.
And this,
will happen while the Tokyo market is open.
For Japanese stock day traders, the earnings release dates of US companies are
‘overseas market events’
but rather,
‘important event days for Japanese stocks’
are they not becoming?
■ Algo trading will also change
So, if US stocks and Japanese stocks are connected in real-time, will the unnatural price movements unique to Japanese stocks decrease?
I believe that
in some areas, there is a possibility they will decrease
.
Until now,
‘Only Japanese semiconductor stocks are being sold off abnormally’
‘Isn’t this an overreaction no matter how you look at it?’
were things that happened.
As long as US stocks were closed, it was difficult to compare whether that was the correct price.
However, if US stocks are moving at the same time,
NVIDIA is barely moving, but
Advantest is down 7%.
If this happens,
‘Isn’t it a bit oversold?’
It also becomes easier to make that judgment.
Arbitrage trading will also become easier to enter.
In that sense, there is a possibility that extreme price distortions that used to occur only in the Japanese market will become less likely to last as long as before.
■ But that doesn’t mean the market will become calmer
I think it’s better not to misunderstand this point.
A reduction in price distortions and
the stock market becoming calmer
are completely different things.
Rather,
the speed of price movements may increase.
For example, at 1:03 PM Japan time.
NVIDIA suddenly drops 2%.
Then the algorithms react.
Sell NVIDIA
↓
Sell NASDAQ-related futures
↓
Sell Nikkei 225 futures
↓
Sell Advantest
↓
Sell Tokyo Electron
↓
Sell semiconductor ETFs
This happens in a very short amount of time.
It’s not that the algorithms will disappear.
Rather,
algorithms that were only operating in the Japanese market will now connect to the global market.
Perhaps it is better to think of it that way.
■ The monitors of Japanese stock day traders will also change
Until now,
Japanese stock order books,
charts,
Nikkei Stock Average,
Nikkei futures
were enough to trade with.
However, from now on, for example, if you are day trading Advantest,
Advantest
alone might not be enough to watch.
On the side,
NVIDIA.
NASDAQ/SOX-related indices and futures.
Nikkei 225 futures.
Dollar-Yen.
In some cases, Micron or Broadcom.
You will need to watch these things simultaneously.
In other words,
**’Why was Advantest suddenly sold off?’
instead of looking at Japanese stocks to find the cause,
‘NVIDIA has started to collapse, so it might come to Japan too’
think ahead. **
This is where things will change significantly.
■ This is not all bad news for day traders
Actually, I think there are quite a few parts that will become more interesting.
Opportunities will increase for those who can understand information quickly.
For example, earnings-related information for Microsoft is released during Japanese trading hours.
They are further increasing their AI capital investment.
NVIDIA starts to rise.
At that moment,
I think,
‘Which Japanese stocks will this ripple out to?’
Is it Advantest?
Is it Tokyo Electron?
Is it data center-related?
Is it electric wire?
Is it optical communication?
People who only look at the Japanese stock order book will think,
‘It suddenly went up. What happened?’
and search for the reason.
However, for those who are watching the US market at the same time,
there is a possibility that they can understand the reason for the price movement first.
This will likely become a major weapon for day traders.
■ However, it is dangerous to assume ‘US stocks moved = buy/sell Japanese stocks’
There are also some points to keep in mind.
Even with 23-hour trading, it does not mean that trading volume will be the same as the regular New York market for all 24 hours.
US stocks moving during the daytime in Japan have, compared to regular trading hours,
a thin order book.
a wider spread.
the potential to move significantly on small orders.
These things are also possible.
Therefore,
NVIDIA is down 3%.
So, I will sell all my Advantest shares.
Such simple trading is also dangerous.
What becomes important is,
to look not just at price movements, but also at trading volume.
‘Is it a 3% drop where a truly large amount of capital moved?’
Or,
‘Is it a 3% drop that moved on small orders during a thin time period?’
It becomes necessary to distinguish between these.
■ Japan’s lunch break will also become a new risk
Another interesting point is,
the Tokyo Stock Exchange lunch break.
Trading of Japanese stocks stops from 11:30 AM to 12:30 PM.
However, US stocks do not stop.
For example, at 11:40 AM.
NVIDIA suddenly drops 4%.
Japanese stocks cannot be sold.
And then at 12:30 PM.
The afternoon session begins.
Advantest and Tokyo Electron gap down all at once.
In other words, from now on,
not just the ‘morning gap’ but also the ‘lunch break gap’
may also need to be taken into account.
■ Not all Japanese stocks are affected in the same way
Of course, not all stocks move in real-time with US stocks.
Those with particularly significant impact are
semiconductors, AI, data centers, electronic components, automobiles, and large-cap export stocks
and other stocks connected to the global market.
Conversely,
small-cap stocks centered on domestic demand,
stocks that move based on their own unique supply and demand,
or stocks where major shareholder sales or margin buying balances influence the share price,
The impact of 23-hour US stock trading will likely be limited.
■ And perhaps the biggest change will be in ‘morning preparation’
Until now, the morning for Japanese stock investors began with…
Last night’s NY Dow.
NASDAQ.
SOX Index.
NVIDIA.
Dollar-Yen.
Checking these was where it started.
However, from now on,
‘How was it last night?’
will no longer be enough.
Even after checking in the morning,
while the Japanese market is open,
‘How is the US moving right now?’
will become necessary to watch.
And one more thing.
To the list of things to check every morning,
‘Who has earnings in the US today?’
will be added.
Is it NVIDIA?
Is it Micron?
Is it Microsoft?
Is it Amazon?
Is it Alphabet?
Is it Meta?
Because that company’s earnings report
could determine the price movement of Japanese stocks that day.
■ N+ Perspective
I don’t think this move to 23-hour US stock trading
is just about
‘being able to buy US stocks during the Japanese day’.
What is even more significant is that
the ‘time lag’ is gradually disappearing from the stock market.
Until now,
Tokyo would receive what happened in New York the next morning.
Europe would receive what happened in Tokyo.
That was the kind of market it was.
But from now on,
markets around the world will move simultaneously,
The same news,
at the same time,
is being priced in simultaneously by algorithms and humans.
Japanese stocks are entering that mix as well.
In other words,
from an ‘era of watching yesterday’s US’ to
an ‘era of watching today’s US’.
For Japanese stock day traders,
it is not just a matter of extended trading hours.
The very standard for viewing the market is changing.
I believe this is actually the bigger change.
And from December onwards,
when Advantest or Tokyo Electron move suddenly,
the first screen you look at will not be Japanese stock news, but rather,
‘What is NVIDIA doing right now?’
Such an era may truly be beginning.
*This article is a personal reflection on market structure and does not recommend the buying or selling of any specific stocks.