Comment It won't work.. second entity can short (Score 1) 342
Even the 500ms won't work. HFT have a lot of infrastructure and resources. You can simple model your HFT in a way that there are two entities trading, one buys it, if the HFT system decides to sell it and is restricted to do so for 500ms or a week, the other entity shorts the same trade, in effect achieving the same results. IMO, you should be allowed to short trades along with this 500ms block for this to properly work.
Obviously, you can have multiple entities trading on behalf of the HF Traders.