Comment on BTST/ATST( Buy/Acquire Today Sell tomorrow)
Risk of short delivery is minimal in Nifty 50 stocks. If you are worried about it, you could just trade using futures.
You get to know by T+2 day afternoon. So if you bought on Monday, by wednesday afternoon.
In case of short delivery, the money from your sale proceeds gets blocked until the auction happens. Which is on the T+3 day, so until thursday evening.