The start of construction keeps getting postponed

And google Corona

Or if you are not looking for search results on epidemiological specifics, just generally for "force majeure" in contract law. Earthworks have a certain key role in a domino effect of deadlines.

The only important thing is the guaranteed completion date

That hardly matters either, what do you want to do if it is not met? Years of legal disputes? Probably not.
Sometimes a penalty clause is agreed upon, but usually only up to 1-2%.. you can't really buy anything with that either.

That hardly matters either, what are you going to do if it’s not complied with? Years of legal dispute? Probably not.
Sometimes a contractual penalty is agreed upon, but usually at most 1-2%... you can’t really buy anything with that.

For an amount of around five figures, I could think of quite a few things...

I just discussed a contract draft with a lawyer. He says that penalty clauses probably won't help us in the current situation either. Finding "grounds outside his risk sphere" should not be difficult for general contractors and others at the moment. According to the lawyer, one will only know for sure in about 2 years when the lawsuits are in court. Important for new contracts accordingly: long price fixation & pay attention to standby interest at the bank and increase the periods.

At the moment, it is pointless to insist on any appointments, etc. It will happen differently anyway. Yes, it is unfortunate for all parties involved, but unfortunately, that cannot be changed now.

Do you get the impression that they don't want to or can't? Are you aware of how the finances of this company look?