Does anyone know if NYSE specialists are required to fill your market orders if they are sent by the close (i.e. 3:59:45) ? Is there a limit to the size they are required to fill (relative to the day's volume, average volume, etc.) Thanks.
If your order gets there before the close, it will be filled. If the order causes a market imbalance, the stock could be halted, and trading could possibly not resume until the next day.