"Jó napot" is actually a little old fashioned - or at least a little formal. I would only use it as a joke with people I know - and they rarely use it to me or anyone they know.
If you allow "Good morning" - how do you differentiate it from "Jó reggelt"? If you allow "Good afternoon" then it will make some people believe it only gets used - in the afternoon.
Here in NZ "Good day" (usually slurred to "gidday") is normal, common and not old fashioned. You will hear it way more than "Hello". (and "Good afternoon" is only used as a telephone greeting)
In the last few exercises of this first basic lesson, the word "jó" offers no possible translation, by lacking the option "good" as a direct translation, and presenting instead others non related words like "wine", "unfortunately" or even twice the word "hello". There is no way of submitting a correct answer like this, and strangely these are repetitions of the same exercise, but with the wrong sugested words for the translation