That's stupid. You only need to delay settlement by seconds, force the buyer to hold for 6 minutes, and the HFT system is broken.
Or you could levy a truly minimal transaction tax, even processing fee for orders executed in than 250ms from offer to buy to re-offer... Maybe.
But thinking you should force holding stock for days means you need to suspend trading when any news breaks. Which halts the market.
Just slow HFT by milliseconds.
Oh, and audit brokers. If they persist in offering stock they actually don't have, perhaps that's a problem? This whole episode sounds like NASDAQ, except they seem to have the stock.