> This is becoming less and less true every day. 24/7 markets are coming whether you want them or not

This has still to exist for real. Every couple of years there is a resurgence of "we should have 24/7 equity markets", followed by milestone announcements of Nasdaq.

The reality is more... nuanced.

First, there has to be a wide enough window for corporate actions and news dissemination to happen. Not only is that a regulatory requirement, but anyway no sane investor would like to trade in such a window even if possible.

Second, there are already early sessions, pre opening sessions, and late sessions on most American markets. The liquidity there is almost inexistant, so I wouldn't say there is a huge demand for extended trading hours by non-retail participants.

And last, half the liquidity of US markets is not on lit books, and half the remaining lit liquidity is close to the auction. I don't think it would even be a net profit for lit exchanges to extend their hours in these conditions. As for dark pool, I think only 2 or 3 of the smaller ones are 24/7, like the one from IB.

> if you're not trading outside of US Equity hours you're leaving significant money on the table

HFTs need a lot of liquidity and tight spreads, that's pretty much only doable at scale in the US and Japan. Europe and EM are either not liquid enough, or only really able to sustain low capital ad-hoc strategies.

Genuinely curious - would 24x7 low-latency trading matter then? Wouldn't after-hours trading (for your local timezone) be happening on an exchange in another location?

Or do you mean dark pools/private exchanges that may run 24x7?