Civil service pension and job

I know it’s early but I like to be prepared plus everything you read tells you to plan ahead. I have a civil service pension which will pay out on 15/01/2025 for an annual amount of around £12500. I currently work around 40 hours ish per week and am hourly paid earning around £18000/annum. When my civil service pension matures in January 2025 I intend to reduce my hours of work by 50% and earnings will naturally be 50% less but will be topped up by my pension. I could of course wait until the end of the tax year before I reduce my hours of work if it makes any difference? My questions; Do I need to inform the tax office of my civil service pension and should I split my personal tax allowance especially having already been earning in this tax year before I get my pension? Does it make any difference me waiting until April 2025 before I reduce my hours? Thankyou everyone for your thoughts and guidance

Hi fallguys12000 Clark,
HMRC will be notified when you take your pension. due to the time of year that you intend to retire, your salary will have already used your full personal tax allowances (based on current figures) so there won't be any available to go towards your pension.
For the start of the new tax year that April, you can split your allowances. this would automatlically be allocated against your  salary first so if you wanted it different.
You can do this through your personal tax account
Personal tax account: sign in or set up
You will need to contact your payrol department about the effect of reducing your hours earlier and how this affects your pension. 
Thank you.