Automatic indefinite leave to remain

I am an EEA national which means that after five years I got automatically indefinite leave to remain without applying for it.
My question is when exactly do you get automatic indefinite leave to remain? Is it 5 years after you first entered the UK or is it 5 years after you are registered with Home Office and joined Accession State Worker Registration Scheme. They ask about the date on AN form and I don't know what date to put
thanks

You do not get ILR automatically, ever. What EEA citizens and their dependants get is Permanent Residence. It has the same status as ILR, but is granted under EEA Regulations automatically. ILR has to be granted by the Home Office and is never automatic.

If you are the citizen of an A8 country, you are only treated as having worked in the UK if you registered with the WRS (only applicable before May 2011). So it would be five years after you registered with the WRS.

So, the earliest you can register for citizenship is six years after having registered for WRS.

Does it mean that I have to apply for ILR before I apply for UK naturalisation? AN form clearly asking about date when I was given ILR not about permanent residence status. I have been living in the uk since May 2004 and registered with WRS since July 2004. My nationality is Polish.

No. You do not need ILR. PR (Permanent Residence) is analogous for the purpose of citizenship. So, you can use the date that you earned PR instead.

You will have earned PR by working (or seeking working) for a continuous period of five years. Any continuous five years between 2004 and 2014 can count.

You will need proof of that. P60s are normally sufficient proof.