At our place, the masonry work was covered daily. It can also rain in summer. Only the frost is annoying, but as soon as the foil is on it, the construction is safe.
I don’t know, doesn’t it even do a shell construction (in solid construction) good if it can "dry out" open over the winter?
However, I personally would also hesitate to have concrete work done at sub-zero temperatures. Possibly there are means to allow the concrete to be processed and dry out even at sub-zero temperatures?