Construction is continuously delayed - call the site manager?

Ha right. Usually there's still something in there about bad weather blah blah uncontrollable circumstances can delay completion.
With you too?

So bad weather must first be defined and then also reported (--> look in the contract!).

Hello, in the fine print it very likely says that the bad weather period is not included in the construction time. Therefore, the 26th of November is more likely to be expected. And usually, the sums are such that the construction company can afford 1-2 months, and you might then be credited with 1000€ for the delay. That way you would still be fully on schedule. Currently, however, it is really difficult to get the companies started. Better to wait a little and get the known subcontractor than have your site manager just take the Yellow Pages out of desperation and pick the first one willing to do it for the money.

The craftsmen had, especially in the outdoor area, a real backlog of orders that they are now working through... of course, this affects all trades.

A landscaping gardener in the circle of friends almost went crazy. 6 weeks at home

Oh right. Usually it also says something about bad weather blah blah uncontrollable circumstances can delay the completion. Is it the same for you?

Yes, something like that is in our contract. But regarding bad weather there are BGH rulings. Bad weather is defined there. According to this definition, based on our records, I come to 3-4 weeks. If it ever becomes a point of dispute, the matter will end up with a lawyer anyway.

I recommend you to stay a bit calmer and not scare all the horses at once. The construction is still ongoing. And yes, the company will surely want to claim more than 4 weeks of bad weather, and in the end, only a judge can settle that. But do you want that, especially since the amount in dispute will not be high. You should also not apply the standards from the rtl2 construction series where entire houses are built within 7 days.