Minimum notice required to leave?

Hello, I have a tenant who on the 25th Oct informed me she would be leaving on the 31st Oct 2023. She is on an AST that started on the 1st May 2023 and would be due to roll over on the 1st Nov 2023.

The tenant pays their rent per month and is up to date with their payments. The AST states the start date is the 1st May 2023 and would run for a period of 6 months from that date, there is no clause referring to a notice period. However, on 9th Oct, I texted her asking if she would be leaving at the end of Oct, and she replied she would be staying on.

On the 24th Oct she texted me asking if she could stay on until the end of Nov and this was agreed. The next day on the 25th Oct she texted me to say she would be leaving on the 1st Nov 2023.

So my question is, what is the minimum notice period (I assumed it was 1 month) a tenant must give before the fixed term expires? I just feel 5 days’ notice is too short.

Many thanks,

Roy