> Warren Buffett proposed that the stock market should be open less frequently

This will result in another market where deals will be made and then finalized on that 'official' when it opens. It's like with employee stock. You can sell it before you can...

Not if we disallow it. We have laws in place to try and prevent a lot of natural actions of markets.

Instant biggest black market of all time, corruption skyrockets, only the richest people get fair deals on investments.

They'll get better than fair deals. They will almost exclusively own all the available pricing information.

> It's like with employee stock. You can sell it before you can...

I thought that this was explicitly forbidden in most SV employment contracts? "Thou shalt not offer your shares as collateral or (I forget the exact language) write or purchase any kind of derivative to hedge downside.' No buying PUTS! No selling CALLs! No stock-backed loans!

Or do people make secondary deals despite this, because, well, the company doesn't know, does it?

AIUI the point of HFT isn't to trade frequently, but rather to change offer/bid prices in the smallest possible steps (small along both axes) while waiting for someone to accept the offer/bid.

most trading volume already happens at open or before close.

Seems like a testable hypothesis. Choose the four times a year that the stock is at a fair price, and buy when it goes below it and sell when it goes above it?

Why shouldn’t people be allowed to do both? I don’t see much of an advantage to making the markets less agile.

It would be nice to be able to buy and sell stocks more than once a quarter, especially given plenty of events that do affect the perceived value of a company happen more frequently than that

The value of a stock usually doesn't change every millisecond. There doesn't seem to be a huge public need to pick winners and losers based on ping time.