Daisy, I traded PHOT through Schwab with a limit o

Daisy, I traded PHOT through Schwab with a limit order without broker assistance after it went on the gray market, so it is indeed possible. (I traded to get out after it was delisted.) However it took two days for the order to fill, and that was while there was still some reasonable volume. The reason is simply lack of liquidity; there's a queue of orders and no volume to fill them.