The base slab has now also become really misshapen and certainly no longer flat... see [Bild 3], in the middle barely any water, on the outer sides almost a hand's breadth deep water.
Therefore, I consider the thunderstorm downpour to be harmless. The reaction process has started. The concrete has not turned to mush and run apart. The water does not harm the reaction. It is very hygroscopic; it already takes what it needs as a reagent. The rest will dry off.
Your word in the ear of God, but I have learned that concrete does not set properly anymore if the binder is washed out, which can be seen by the cleanly washed pebbles. But no question, of course, I would prefer if everything is correct.
I also still see a difference between a thunderstorm downpour and heavy rain. In the pictures, you can see what craters the drops leave on the water surface when they hit. They were thick and very fast!
I'm just worried about the words of the floor slab construction manager. An hour before the heavy rain, he said a little rain would be a great post-treatment, but rain like yesterday would be really bad.... Sure enough, we had the heavy rain like yesterday.