Temporal complement and its correct case

Question

I'm confused about the correct case to use in a temporal complement: do you need the accusative?

I'm asking about the expression of a well determined time (that does not continue). Examples may be:

In summer I always go swimming

Last December, it snowed a lot

You'll have a job in 2014

Answer 1

Time indications including nouns are often introduced using a preposition (in, an). If we are talking about a fixed point in time, the preposition will need Dative.

There are many instances of time indications that don't have neither preposition nor article:

Letzten Montag war ich schwimmen.

Nächstes Jahr fahre ich in den Urlaub.

Diese Woche habe ich frei.

Those are in Accusative.