It is so often the same with communication. It is completely unclear whether there is a problem at all and if so, what kind of problem it is. The only thing that becomes clear is that you are nervous and lose sight of your goal:
You insist that the civil engineer must start immediately. But the only interesting thing to know is that he will finish on time. In the next three weeks, this is still feasible, and the civil engineer can certainly explain to you how if you ask accordingly.
Instead of approaching the civil engineer with this simple question, for example: "I am a bit nervous because nothing has happened on the construction site yet. How confident are you that you can finish on time?" you go to him and "confront" him with weather data, which you as a layman cannot even assess in relation to concrete construction (e.g. moisture as wrote). Of course, your civil engineer considers you a know-it-all.
Surely the civil engineer could also have communicated actively and informed you about the impact of the weather on the goal of meeting the deadline.
Running to a lawyer with the completely unclear situation of whether everything will be finished on time is ridiculous and only brings money to the lawyer without improving anything.
Canceling the contract for work – why? It is still unclear whether the contract can be fulfilled without any problems.
Moreover, you will now definitely miss your goal of meeting the deadline with a change.
Panic is a bad advisor for builders.
Anyway – this is a bad start. You can always still ask the above question. Maybe it will clarify a lot.