We have these in Europe & the UK now with MiFID II, on several venues

They are called Periodic, or Frequent Batch, auctions.

This paper & earlier works it's based on were very influential in the design and regulatory framework for these: https://academic.oup.com/qje/article/130/4/1547/1916146

Here's a good intro to them: https://www.fca.org.uk/publications/research/periodic-auctio...

Volumes are small relative to the market as a whole, but execution quality is very good.

> WHY???

Shouldn't the question be "why not"?

More APIs than not on this planet are considered business critical and doesn't just close. Stock markets are strange as they must be highly available for a few hours and then can be shut down for the day. Imagine if AWS closed every night.

A lot of Amazon retail does close every night. You can put in a request but it won't be fulfilled and shipped until morning. Getting rid of that is a nice idea, but also "instant fulfillment" is not great either without "instant returns." The idea of "instant trading" seems like it can instantly put the system into a bad state with no recourse to fix it.

AWS doesn't close, which was the example.

The real reason stock markets close is because financial institutions are very interested in keeping it that way. It is lucrative to play pretend stock markets after hours.

(This is a very real question all over Europe right now, and it is interesting to see which institutions talk the loudest about how beneficial a shortening of opening hours would be to just about everyone.)

>WHY???

The exchange wants to make more money, and people want to be able to trade at whatever time they feel like.

It turns out they don't; they really want to meet their benchmarks, and trade where the liquidity is.

One data point - 40% of the French stock exchange's turnover is now in the closing auction. Other markets have a similar trend. Longer trading hours mean thinner liquidity throughout the day, and the direction of travel in Europe is strongly towards shorter trading hours.

The answer is also “foreigners”. Regular working hours for a German exchange can produce some pretty brutal trading hours for say, London. When I worked in finance they started serving breakfast at IIRC 5am, since some trading desks started their day then and ended around noon. Expanding those hours can entice foreigners to trade during non-insane local hours.

> Regular working hours for a German exchange can produce some pretty brutal trading hours for say, London.

Berlin and London time are only off by one hour.

You probably meant the US instead of Berlin/London or there is something going on I'm not aware of?

Yes; I picked the time zones out of thin air, and I chose poorly.

Tradegate is even 08-22...