Ann: March 2020 Quarterly Report, page-50

https://www.epa.wa.gov.au/proposals/lake-way-sulphate-potash-project

Sounds like you have checked out the link above.
My understanding stems from following RWD.
Generally either the EPA (in case of RWD as first mover?) or proponent draws up the scoping document.
The company then produces the ERD based on the SD.
The ERD is then assessed by the EPA. There is no public review for SO4.
Stage 4 is the EPA decision and 5, the minister’s signature.
From memory the scoping document includes an intended timeline for the whole process.

I think it is fair to say that the original timelines for RWD and APC have proven to be grossly inaccurate.

So theoretically SO4 need to produce a SD and ERD. The last quarterly stated that the ERD was close to completion. Presumably the EPA has seen a SD and the scope of work required was less because of existing approvals.https://www.epa.wa.gov.au/proposals/beyondie-sulphate-potash-project
The KLL ERD assessment was completed 2 months after submission with minister approval 2 months later:


It appears that it takes time for parties to reach agreement on an acceptable ERD. APC said they had lodged their ERD back in November yet it still wasn’t on the EPA site last time I checked.

It is reasonable to suggest that SO4 could get the nod 2 months after submitting an ERD that satisfies the EPA. And then a couple of months before the minister signs off assuming there are no successful appeals.