It's humans from other banks/funds bidding on the block of stock. As far as timing, for this situation it's basically overnight for regulatory and price reasons

It's humans from other banks/funds bidding on the block of stock. As far as timing, for this situation it's basically overnight for regulatory and price reasons. Regulatory because there are legal margin requirements for levered positions and you can't handle the price going much lower, and price because if you had to sell this on the open market you'd keep selling shares for less and less. So JPMorgan/Goldman prepare all the info on the book and start calling institutional investors after the market closes. The funds and banks prepare bids, there's some negotiation, and the block is finalized before trading opens the next day. Speed does matter, but you're only calling investors you know "can" close the deal (i.e. they'll have enough capital to buy it all that day/night). So it's more of a price question than a speed one at that point? And really, nobody wants the downward spiral of a fire sale in the tech sector. Someone will make money on that chaos, but it's a lot of risk when you can lock in a discount with the block trade.