The Sentinal Achievement - how?

There seems to be lots of conflicting info out there, but I’ve been trying to get this achievement for days now.

I stayed in a building on an extreme planet for many SOLs, I built a base on an extreme planet and stayed there for many SOLs, I’ve stood out in storms for what seems like days.

Yet my Extreme Survival stays on 4.7 SOLs.

What’s the deal here?!

EDIT: I haven’t died on this save.