5 years counting for application date (Visa/BRP/Arrival?)

My very first BRP was issued 2 weeks before the 'Valid From' date of the Tier 2 visa stamped into my passport. I arrived in the UK about one week after that 'Valid From' date.

Does anyone know if I can start counting 5 years for the ILR application date from the BRP issuance date or it should be from 'Valid From' date on the Tier 2 visa? Or it rather should be from the date when I actually landed here?

Use the earliest visa approval date, so the earliest date on either the BRP or the sticker