ETFs - When do you pay the Deemed Disposal Tax?

If i buy an ETF today (Jan 6th, 2025), the deemed disposal tax becomes due on Jan 6th, 2033.

How long from Jan 6th, 2033 do I have before I must pay the tax? Is it 30 days, or is it, you must file a return no later than November 2033?

Assuming you are currently a PAYE taxpayer, then beginning in 2033 you will become a chargeable person and must register for self-assessment.
Your preliminary tax payment will be due by 31st October 2033, but since this is your first year of self-assessment the amount will be nil.
Your 2033 tax return must then be filed the following year by 31st October 2034 and the tax payment will be due on the same date.