Can the margins released from selling my MTF holdings be used to take new positions ?

If the margins are from pledged collateral, they are released and added to your buying power immediately on T day, allowing you to take further positions the same day.

Example: Mr. Girish has an MTF position worth ₹2,00,000, backed by ₹50,000 stock collateral margin. He sells these holdings for ₹1,90,000, incurring ₹10,000 loss. On T day, ₹40,000 (₹50,000-₹10,000) is released and added to his buying power. He can use the ₹40,000 to take new positions on the same day. 

However, if the margins are from the cash component, they will only be added to your buying power on T+1 day, meaning further positions can be taken only after that.

Example: Mr. Girish has an MTF position worth ₹2,00,000, backed by ₹50,000 cash margin. He sells these holdings for ₹1,90,000. The ₹40,000 (₹1,90,000 - ₹1,50,000) will only be added to his buying power on T+1 day, and he can take new positions only after the update on T+1 day.