Selling and then buying holdings on same day

Recently I sold and bought back my holding(>T+2) stock on the same day and I noticed there was no T1 header on it, so I suppose no Demat transaction takes place and my long term holding period doesn’t get reset?

Also if I buy some shares with CNC option and sell them on the same day but after 3:20 pm (intra square off time), is it considered as BTST or intraday?

Right, selling shares from your holdings and buying back the same day will be considered as an intraday trade. This doesn’t have any effect on your holdings.

This will be considered as intraday trade only.