When to make the move?

[ChickenCanoe]

To reiterate what Ridgerunner said, replicate a mother hen. Provide a toasty spot and the rest of the area cool.
A mother hen doesn't heat all the ambient air. Regardless of outside temperatures, she lets them warm up under her and then they run around in the cold.
That's best for chicks.
The 90-95 F the first week thing and lowering 5 degrees each week is really appropriate for large operations with thousands of chicks. For a few chicks, I replicate nature.

 

[Ridgerunner]

Until they are feathered out, probably around 5 weeks, they need to be out of the rain, out of the wind, and have a warm spot to go to so they can warm up if they need to. Looking at the photos, it looks like that closed-in elevated part has nests, a roost, and room for feed and water. As you said it is not finished so I don’t know what it will look like in the end or how closed in it will be.

I understand that you are in southern California. Nice climate. If you can come up with a way to keep them out of rain and wind while providing them a warm spot to go to when they need to, you can manage, whether that is at ground level or in the elevated part.