Learn Russian: Пекарь делал тесто двадцать минут. - The baker was making dough for twenty minutes.

The sentence focuses on how long the action lasted (for twenty minutes), which requires the imperfective aspect. If the sentence meant 'finished making the dough in twenty minutes' (focusing on completion), we would use the perfective сделал with the preposition за.

Why is there no Russian word for 'for' in the phrase двадцать минут?

To express how long an ongoing action lasts, Russian simply uses the time expression in the Accusative case without a preposition. Adding the preposition за would change the meaning to 'in twenty minutes' (time to completion).

Why is the word for minutes spelled минут here instead of минуты?

After numbers ending in 5 through 20, including двадцать (twenty), nouns must be in the Genitive plural case. The Genitive plural form of the feminine noun минута drops the ending, becoming минут.

Is the word тесто in the Nominative case here?

It is actually in the Accusative case because it is the direct object (the thing being made). However, since тесто (dough) is a neuter noun, its Accusative form looks exactly the same as its Nominative dictionary form.