This is effective 7 July 2023 (Friday). All existing contracts with be revised on 6 July 2023 EOD so the first Friday expiry will be 14 July 2023. If Friday is a trading holiday, the expiry will occur on the previous trading day. Monthly contracts will expire on the last Friday of the month versus the last Thursday of the expiry month.
As a reminder, BANKNIFTY expiries on/after 27 July 2023 will have the updated minimum lot sizes of 15 (instead of the prior 25).