What are pre market and post market sessions and orders?
Pre-open session: NSE started the concept of the pre-open session to minimize the volatility of securities during the market open every day. Between 9:00 AM to 9:15 AM is when the pre-market session is conducted on NSE.
During the pre-market session for the first 8 minutes (between 9:00 AM and 9:08 AM) orders are collected, modified, or cancelled. You can place limit orders/market orders. The order collection window can close at any time between 9:07 AM and 9:08 AM.
After closure of the collection window to 9.15 AM new orders cannot be placed. The orders placed are matched and trades are confirmed. You can place orders during the order collection period only on the equity segment. Read more here.
Post-closing session: Similar to pre-market orders, post-market orders are allowed only for equity trading. The post-market session or closing session is open from 3:40 PM to 4:00 PM.
During this session, people can place buy/sell orders in equity (delivery segment using the CNC product code) at the market price but do note that even if you place a market order it will be placed on the exchange at the closing price. So for example, if the closing price of Reliance at 3:30 PM is Rs. 800, between 3:40 PM and 4:00 PM, you can place market orders to buy/sell Reliance at market price (will be taken at Rs. 800).
The post-market session is not very active and you can look at the movement of stocks by opening the Marketwatch window from 3:40 PM to 4:00 PM.