There's one thing that always baffles me about this kind of market work. Let's for the sake of argument assume that HFT and other sophisticated market making activities are crucial for price discovery and other great social benefits. Then why does this amazingly important social good get mostly turned off over 80% of the time[1]? Even as a retail buy-and-hold investor in boring ETFs not being able to trade outside normal office hours is an inconvenience. Surely the world economy has even more uses for trading at all hours than me?
[1] https://www.nyse.com/markets/hours-calendars