A pre-open market session is used to determine the ideal opening price for a stock for that particular trading session. The pre-open market session is from 9:00 am to 9:15 am (15 minutes) after which the trading session starts on NSE and BSE. The order collection, modification, and cancellations happen between 9:00 am to 9:08 am. The orders placed are matched and trades are confirmed after 9:08 am.