"I am going to my grandmother's in an hour."
Translation:Idę do babci za godzinę.
Does 'Za' have two meanings? i have only seen it used as 'behind'.. but in this case it means 'in' (refering to time). And if it does mean 'in' can someone clarify if its only used to refer to time or also space. Also the case of the noun with this meaning.? sorry for asking a very easy question, but as of the moment there are no notes to understand
As most prepositions, "za" has several meanings. "Behind" is indeed the most important and most popular one. Polish Wiktionary list ten different meanings. But at the level of Duolingo learner, I guess it's probably enough to know the four that are mentioned on English Wiktionary. This one can go under option 4, I guess, but it's a normal Polish construction to say that something will happen after a given time.
Jest 20, mecz zaczyna się o 21. = Mecz zaczyna się za godzinę. (It's 8PM, the game starts at 9PM. = The game starts in an hour.)
As for space, as you can see there are two options. One is the simple 'behind' you have mentioned, and takes Instrumental:
Jestem za domem - I am behind the house.
The other denotes movement 'to behind somewhere', and takes Accusative.
Idę za dom - I am going behind the house.
Yup. Well, usually one visits one's own grandma rather than someone else's, right? So why mention it, if it's a logical assumption? Of course, you can be specific and say "swojej/mojej babci", but there's absolutely no need. If you really are going to someone else's grandma, then you specify it.
Actually, this is one of the rare examples when even English, which normally loves possessives (I am putting my hand in my pocket), doesn't need it. We will change the main version to just say "grandma's".