Would it be really used exactly like that, when the visit in mention is a visit at your grandparents' house? It seems kinda weird to me, although I may be wrong.
Because I don't think an appointment with a dentist, or a school headmaster, or a lawyer could be called 'a visit'.
I thought that "visit" corresponds to "wizyta" and "spotkanie" translates to "meeting/appointment".
I am not sure about the meaning of this sentence in Polish. How can I apply it? Is it something like "Kiedy jest twoja wizyta u lekarza?" ?
Visit/appointment usage also depends on context: https://goo.gl/nSRFpT For lawyers situation is different.
After giving it more thought, maybe 'spotkanie' really takes most of the appointments (and definitely meetings), but at least with all types of doctors "wizyta" seems to me like the most, if not the only, natural choice. Spotkanie z lekarzem would sound to me as if you were going to a restaurant together.
Yes, your Polish question is alright. I myself would ask "Kiedy będziesz miał wizytę" - "When will you have the... visit/appointment".
Oh, I'm also reporting your version because I'm now persuaded that it should be correct.
It is worth noting that in spoken Polish you would rather say "Kiedy masz wizytę?", literally "When do you have (your) appointment?" Another version: "Na kiedy masz wizytę?" (literally: For when do you have (your) appointment).
This sentence feels a bit unnatural and sounds like a direct translation of the English sentence.