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What is periodic call auction & why are some stocks traded in this category?

Periodic Call auction was introduced by SEBI in 2013 to curb volatility in illiquid stocks. Stocks that qualify the criteria of illiquidity is explained in this SEBI circular such as the average daily number of trades of less than 50, the daily trading volume of less than 10000, and a bunch of other such conditions. 

There will be 6 call auction sessions conducted in a day starting from 9.30 AM of 1 hour each. The call auction window for trading is similar to the pre-market session conducted for equity stocks. There will be a 45-minute window for order placement, modification and cancellation. All orders are accepted and matched in the next 8 minutes, trades are confirmed. There will be a 7 minute buffer period before the next call auction session. 

Session NoStart Time- Order PlacementOrder Matching Buffer Period
19.30 AM- 10.15 AM10.15 AM- 10.23 AM10.24 AM to 10.30 AM
210.30 AM- 11.15 AM
11.15 AM- 11.23 AM
11.24 AM to 11.30 AM
311.30 AM- 12.15 PM
12.15 PM- 12.23 PM
12.24 PM to 12.30 PM
412.30 PM- 1.15 PM
1.15 PM- 1.23 PM
1.24 PM to 1.30 PM
51.30 PM- 2.15 PM
2.15 PM- 2.23 PM
2.24 M to 2.30 PM
62.30 PM- 3.15 PM
3.15 PM- 3.23 PM
3.24 PM to 3.30 PM

So yeah, if the idea is to buy/sell such illiquid stocks which are on Periodic call auction, you need to place your orders in the first 45 minutes, and you will be able to buy/sell based on if your order matches in the next 8 minutes.

Refer to this NSE circular & this BSE circular for a more detailed explanation.