Learn Hardcore German: Trotz des Regens hatten wir ausreichend Zeit, das Formular gründlich zu lesen. - Despite the rain we had enough time to read the form carefully.

The preposition trotz requires the genitive case in standard German, so you need des Regens (genitive singular of der Regen). Colloquially many speakers say trotz dem Regen (dative), but in formal writing you should use the genitive.

Why does ausreichend appear without an article or adjective ending before Zeit?

Here ausreichend functions as a quantifier (like viel, wenig, genug). Quantifiers act like determiners and do not take adjective endings or need an article: ausreichend Zeit = “enough time.”

What case is Zeit, and why is it in that case?

Zeit is in the accusative case because it is the direct object of the verb hatten. In wir hatten Zeit, Zeit is what is being “had,” so it appears in the accusative.

What is the function of das Formular gründlich zu lesen in this sentence?

It’s an infinitive clause with zu that serves as a complement of Zeit haben. It tells you what we had time for—namely “to read the form thoroughly.”

Why is there a comma before das Formular gründlich zu lesen?

Since the 2004 punctuation reform, commas before zu-infinitive clauses are optional. You can drop it if the sentence remains clear, but including the comma often makes longer sentences easier to parse.

Could we place the adverb gründlich somewhere else in the infinitive clause?

Adverbs of manner like gründlich usually come after the direct object but before the zu-infinitive: das Formular gründlich zu lesen. Technically you could say gründlich das Formular zu lesen, but it sounds unusual.

How would the sentence look if we used an um … zu construction instead?

You could rewrite it as:
Trotz des Regens hatten wir ausreichend Zeit, um das Formular gründlich zu lesen.
This uses the um … zu clause to express purpose in the same way.