29-31 transactions are counted in the next month because settlements take 3 days. It's an HDFC quirk that applies to everything from cash points to annual fee waiver.
For example: My transaction on 29th December 2022 counted for 2023 Q1's milestone. Similarly, my 90k transaction on 29 May 2023 didn't give me any cashpoints yet, it'll be counted in this month.