Some prepositions are used to mark place or direction within sentences. Questions containing the following question words
will be followed by the dative or accusative cases, respectively. But not all prepositions are that high-maintenance. :)
This topic is about prepositions used to talk about times during which or at which certain things might have taken or take place. We advise you to learn them in context and not to worry about the grammar. These prepositions are am, um and im. They are used as follows.
If you insist on knowing the grammar behind the words, here are a few fun facts:
1. Prepositions of time are used to answer the questions "when" or "for how long".
2. Unlike prepositions of place, they don't change the case. Each preposition of time is followed by one case only.
For example, an and in (time) are always followed by the dative.
an + dem = am
in + dem = im