ILR Eligibility: 28 Days From when?

My BRP date of issue was 9 june 2021. It was valid until 31 Dec 2024. I renewed it and got an evisa after that point.

When is the earliest I can apply for ILR?

Is it 28 days from:

1. date of BRP issue?

2. the date of employment?

3. date of visa start?

I think it's number #3 -- but how do I find this out My evisa just tells the date of renewed visa. And I couldn't find it in my BRP