According to the PCA, concrete slabs on ground need 7 days to cure at a temp above 40-degrees F.

Moisture and water along the edges of a slab on grade can, over time, undermine or weaken the slab, particularly if the soils are expansive which many are in the Bay Area.

Step one should be to create positive natural drainage away from any and all slabs, new and existing. Step two is to use gutters, downspouts and splash blocks to carry away roof run-off when the new structure is complete.

If your topography is such that there is substantial surface run off which fall against your foundation, you may want to consider a subsurface gravel and tile drainage system to pick up and remove the water against the foundation.

Hope this helps.

I don't understand what your concern is. What kind of foundation is it? basement, crawl space, slab on grade? If the concrete has already reached full hydration water can't hurt it. If there is an existing foundation without adequate drainage water might get into an existing basement but you can pump it out. The contractor should wait for a reasonable dry period to start the subfloor but it should be Advantech or a similar water resistant material in case it rains again. If the foundation settles because of rain it was not poured on undisturbed soil but poorly compacted fill and it would eventually have settled when the structure was on it.

We are in the same general area, and the concrete guys (who are supposedly very good) pour between the rains and aren't worried about it. We are only working on footings now, so perhaps that's different, but no worries here.