Is the construction time specified in the prefabricated house contract binding?

If the company postpones this point, it is unpleasant, but since we only sign the loan at that time anyway

This will be even worse than if you sign the loan agreement now — at least as far as the construction period is concerned. Assume that in 12 or more months you will have a slightly higher interest rate. A €400K loan over 20 years with 0.20% more interest results in about €15K additional cost. Just provision interest of 3% (?) for a 9-month delay is only €9K.

That will get even worse than if you already sign the loan agreement now - at least regarding the construction interest rates.

Assume that in 12 or more months you will have a somewhat higher interest rate. €400k loan over 20 years with 0.20% more interest amounts to around €15k additional expense.
Just provision interest of 3% (?) for 9 months delay is only €9k.

You are absolutely right, but the interest rate could just as well remain constant or even decrease (unlikely). So in any case, it’s a gamble, but with the current interest rate you could at least consider it.

but at least I don’t assume it says "If the provider does not fulfill their contractual obligations, tough luck for you. Nyah-nyah"

The list from may be correct. However, I don’t necessarily see that it applies to you, or that you can rely on it now.

Although they are bound for about 8 months and then it probably applies, it is only now going into planning, as far as I understand. Appointment for the surveyor, geotechnical report, connection of construction power and water… all that can take time – especially construction power can (I experienced it myself during the building boom in 2013) take up to half a year. If you order it now, the box will sit unused for several months, but you still have to pay.

We just don’t want to be liable for costs that arise due to a delay we are not responsible for and that according to the contract shouldn’t occur.

Since so many small wheels have to be set in motion for the big wheel to turn, many things can drag on.
And that has to be factored in.
By you. These are your costs, including the double burden of rent/installments, standby interest (which can sometimes be negotiated away, etc.). Many pay these, and it is also not unusual to equate them with a delay.

As a starting point, the approval of the building application is set.

That’s right. And you probably haven’t applied for it yet.
The consequence of your personal situation, that you already have to finance the first 10%: plan a buffer into the financing. Because the building loan is not responsible for everything or for double burdens that have nothing to do with delays.

What you read here, a year of planning is not that uncommon.

As a seller, I would not have put them in the contract either.

Without a contractual penalty, a construction completion target is a toothless tiger.

For us, it is also 8 months from the first groundbreaking. The contractual penalty is €200 / day.

Every home builder who offers a completion guarantee from a certain construction or planning progress point knows exactly what they are doing.

The starting signal for the countdown will always be timed so that they can be relatively sure to meet the deadline.
If it says from the building permit, then the building application documents will only be completed when it is foreseeable that the capacities for the next steps are available.
They are not from yesterday either.

And that is fair and reasonable.

With us, it also took a long time after signing the contract, I mean about 4 months, until the architect came by for the rough planning.