I think you'd translate "hello" rather with helló. Or szia, or the very Austro-Hungarian szervusz. "Hello" sounds colloquial, jó napot is more formal. I think "good day" is a good translation, even though it seems to be uncommon in English. How do English speakers greet (formally) throughout the day?
Same in german with "Einen schönen Tag noch, der Herr", but that depends on the context and there is none here at Duolingo. So it is not useful to use word by word translations, because for the translation back to english you always have to remind that duolingo course creator mixup english.
In standard American English, the greetings are 'good morning', 'good afternoon', 'good evening'. On the other hand, when you are leaving the standards are 'good day', 'good night', and 'goodbye'.
'Good day' is often expressed these days as 'have a nice day'. In any case, it is something you would say on parting, not in greeting. (But in Australian English, I believe 'g'day' is used as a greeting.)
In contrast, 'jó nappot' is said in greeting. So although it literally means 'good day', it may be better to translate it as 'good afternoon' or even 'good morning', since 'jó nappot' can be used in the late morning hours. ('Jó reggelt'' is used only in the early morning.)
Native Hungarians, please correct me if I'm wrong.
Basicly you're right! Jó napot is usually a greeting said when meeting, and the parting one is Viszontlátásra or its shorter forms like colloquial Viszlát and very informal versions that are closer to the equivalents of "Hi!". ("Hi", "Hello" and "Ciao" are more and more frequent, and the latter has funny Magyarized forms like "Csá", "Cső", etc. and even surprising substitutes like "Csőváz" or "Csőtészta", originally mean the tubular frame of backpacks and a macaroni-like pasta, used only for its sounding and the surprising effect.)
In Hungarian we use different time segments for the day that English or Italian, etc., closer to the German usage. From midnight to 4am (approximately) is éjszaka (night) but that often counts from about 10pm. From approx. 4am to 9 pr 10am is reggel (morning). About 9am to midday is délelőtt that is still morning in English but literally "before noon". Around noon we often use dél that means both the exact moment of noon and the period from 11:30am to 1pm. The latter is often expressed by dél körül or déltájt, délidőben and their translation could be "around noon". (Dél körül is its literal version.) From 1pm to 5 or 6pm it is délután (afternoon) and its limits depend on the length of daylight. From the end of délután to 9 or 10pm is este (evening) that may run even into midnight in certain subcultures. From the end of este to midnight (éjfél) it is éjszaka once again.
When greet each other, we mostly use the specific times, like jó reggelt for reggel, jó napot for délelőtt, dél, délután, jó estét for evening, and jó éjszakát for the night. We never use jó hajnalt (it is about daybreak), jó délelőttöt, jó delet or jó délutánt.
In general there is a tendency to substitute "jó napot" with szép napot (formal) and legyen szép napod (informal). The first means "Have a nice day" literally, the latter is more personal "may you have a nice day". Sometimes it is used for evening, too, but almost never to night.
A side note: Hungarian photographers often part from each other with szép fényeket! ("Have nice lights") I've heard that Germans use sometimes the similar Gute Licht. Sailors wish each other Jó szelet ("good winds"), pilots sometimes say jó landolást ("good landing").
I wonder that all listeners are impressed by good afternoon and do not see the problem in the second part of sentence.What does it mean ''to which building'' What kind of English would say so.Upon me no one.Please native English comment this text.and translate it to normal English.Thanks in advance