Learn Hardcore German: Die Werkstatt verspricht, dass die Reparatur nur zwei Tage dauert. - The workshop promises that the repair will take only two days.

In German, you must separate a main clause from a subordinate clause with a comma. Since dass introduces a subordinate (dependent) clause here, you place a comma before dass.

Why is the verb dauert placed at the end of the dass-clause?

German subordinate clauses (introduced by conjunctions like dass) follow the “verb-final” rule: the finite verb moves to the very end. That’s why in dass die Reparatur nur zwei Tage dauert, dauert appears as the last word.

Why isn’t there a preposition before zwei Tage, and what case is zwei Tage?

When you use dauern to talk about duration, you pair it directly with a time expression in the accusative case—no preposition needed. So you say dauert zwei Tage (accusative). If you want, you can add lang for emphasis: dauert zwei Tage lang, but you never need in.

Why is nur placed before zwei Tage?

The adverb nur (only) always sits immediately before the element it limits. Here it limits the duration zwei Tage, giving the sense of only two days. Moving nur elsewhere (for example before dauert) would change the focus or sound awkward.

How does versprechen work with a dass-clause? Don’t we need an object?

Versprechen can take a dass-clause as its object when you promise that something will happen. You don’t need an explicit object pronoun unless you want to specify the recipient of the promise (e.g. Die Werkstatt verspricht dir, dass…). Here, the entire dass-clause functions as the object of verspricht.

Why are there two instances of die in this sentence?

Both Werkstatt and Reparatur are feminine nouns, so their singular nominative definite article is die. Die Werkstatt is the subject of the main clause, and die Reparatur is the subject of the subordinate clause.

Could I express the same idea using an infinitive with zu instead of a dass-clause?

Yes. You could say:
Die Werkstatt verspricht, die Reparatur in nur zwei Tagen zu erledigen.
This infinitive construction shifts the focus to the workshop’s action (to complete the repair in two days), whereas the dass-clause promises that the repair will take two days.

Why is die Reparatur not in the accusative even though it seems like the “object” of the promise?

Inside the dass-clause, die Reparatur is not the object of verspricht; it’s the subject of dauert. The entire dass-clause is the object of verspricht, but within that clause, standard sentence rules apply—die Reparatur (what lasts two days) is in the nominative as the subject of dauert.