If you happen to sell equity shares from your demat account, you can only take positions for 80% of such sale credit. This is because, 20% margins are applicable on all equity transactions.
The profits made from intraday equity transactions cannot be used on the day of trade and the next trading day since equity transactions are settled on T+2 day i.e. trade day + two trading days.
Similarly, profits arising from trading intraday in derivatives cannot be used on the trade day and can be used from the next trading day since derivatives settlement take lace on T+1 day.