Genitive of time with or without an article, "Morgens" vs. "eines Tages"

Question

The question is on the instances of "genitive of time" found in this passage from a translation Albert Camus's The Stranger (by Uli Aumüller)

Auf meinem Tisch stapelte sich ein Haufen Seefrachtbriefe, und ich mußte sie alle durchsehen. Bevor ich das Büro verließ, um essen zu gehen, habe ich mir die Hände gewaschen. Mittags mag ich diesen Augenblick sehr. Abends macht er mir weniger Spaß, weil das Rollhandtuch, das man dabei gebraucht, ganz feucht ist: es ist den ganzen Tag benutzt worden. Ich habe meinen Chef eines Tages darauf hingewiesen. Er hat geantwortet, er fände das bedauerlich, aber es wäre doch eine belanglose Nebensache.

It seems to me that, as used above:

• Mittags and Abends refer to a typical afternoon and evening, or most afternoons and evenings. (Accordingly, mag and macht refer to a tendency.)

• eines Tages refers to a particular day. (habe hingewiesen refers to a particular action.)

Let us call this the pattern.

QUESTION

Which of the following is the case?

1. The pattern always holds true. This means:

   • genitive of time without an article (e.g. Mittags) always refers to a typical instance of time in question (be it day, morning or season) and

   • genitive of time with an indefinite article (e.g. eines Tages) always refers to a particular time.

2. The pattern does not always hold true. Meaning:

   • genitive of time without an article can refer to a particular time and

   • genitive of time with an indefinite article can refer to a typical time.

If 2, please give some examples of genitive of time that is off-pattern.

To avoid any confusion, I am excluding genitive that qualifies a noun as in am Mittag eines schönen Tages. The question is on the genitive absolute construction only.

BACKGROUND

This background is not part of the question.

According to the Our Living Language section of this Web page, the of a morning construction is "not used for single actions." If true, that makes English rather different from German in this respect.

Answer 1

Mittags is not genitive, but an adverbial form of Mittag. This means every Mittag. The same holds for Abend and abends. Transforming

Mittags mag ich diesen Augenblick sehr.

would lead to

Diesen Augenblick mag ich mittags sehr. (und nicht Mittags)

although it's not the same intended style. Hence, to answer your question, neither 1 nor 2 hold exactly in their original form, but, indeed, the genitive in eines Tages usually refers to a particular time and the adverbs like morgens, montags, abends refer to recurrent events.