I think this would really only have a meaningful impact if the majority of exchange follow suit and 23 hours trading really takes off and becomes commonplace. Otherwise the volume outside RTH will be very limited as everybody who wants good fills will keep trading during RTH. I can see at least 2 benefits of limited RTH instead of 23 hour trading: 1. 6.5 hour trading concentrates most of the daily volume into those 6.5 hours. All else being equal (i.e. same minimum tick sizes as before, same total daily volume as before, etc.) trading cost [for small to medium orders] would increase. Trading cost is a function of bid/ask spreads, and market maker bid/ask spreads are typically a function of volatility and [trading volume per time period], right? 2. Every situation is different, but some trading strategies / algos that depend on (counterparty) volume would probably require the trader to trade 23 hours instead of the current 6.5 hours to generate the same results (profits). This would affect manually executed strategies (I guess mostly retail traders); automated algos would of course not be affected, because algos and trading bots don't need to sleep. Some retail traders would have to spend almost 4x the time for the same daily profit, or in other words, the profit per hour might be ca. 4 times less. Perhaps not coincidentally, the only products that I am aware of that have near 24 hours RTH are highly liquid index futures and fx, where limited liquidity per hour probably does not matter that much, and/or bid/ask spreads are often at or near the minimum tick size.