Will stocks still gap at the 9:30 AM open, or will they trade like futures, and have no gap? Meaning, will the 9:30 AM open just trade off the 9:29 AM pre-market price. Also, will traders use a 9:30 - 4:00 PM candlestick, as they do now, ignoring the pre-market trading? Or will traders use a 23-hour candlestick like futures?
It's going to trade like any ~continuous market. No gaps ... Most of the trading is algorithmic trading. You might still have more or less volume depending on time. Algorithms can provide liquidity 24/7, They can trade 24/7.
Will we really know until it happens? I say that because isn't Nasdaq already a 24-hour market, yet the stocks still gap at 9:30 AM. I have a feeling pre-market will be illiquid.
No, US markets won't gap much. Gaps are mostly a reaction to things like news/earnings after RTH, Asia markets, Europe markets while the US RTH are closed. The technical "gap plays" will likely fade into the sunset. Could be a "thing" for those who follow markets around the world while US markets are closed. 24-hr markets are not a great thing... nor are they a negative.
If one is a big player, liquidity is always an issue. If markets are thin, should trade with limit orders.
You maybe could do your own pricing with stock quotes outside market hours and then arbitrage with ETFs because they are usually priced within market hours. I think that not all ETFs will be tradable outside market hours and then there is still order imbalance at the market open and market closing. You could trade this to your favor when you do the ETF pricing in your Excel sheet realtime with the individual stocks contained in the ETF and compare the fair value quote versus the actually traded quote for some ETFs, especially at market open and closing.
I'm mostly concerned about end of day data. Most of my strategy is based off candles closing at 4 PM. The new close will be 11:30 PM as per the NYSE announcement. Since the NYSE will resume trading at 1:30 AM, I would have to be awake during that narrow period between 11:30 PM and 1:30 AM to gather data.
If you have intraday data you can create custom bars depending on the software you have. Multicharts and Tradestation does have that feature for example. Then you can have any closing point you need. Also there are templates for during market hours or all hours templates for symbols aswell. It really depends on the data and software.
I guess I should contact Finviz. Currently, their data reflects 9:30 am -4:00 pm. Hopefully it stays that way.
If 24-hour comes to the major stock exchanges, futures exchanges will become irrelevant and there will be no "gaps" in the indices. Mark it, man.