Thanks for this comment papageorge. The distinction you refer to here is very similar to ancient Greek. The second example, αυτή τη νύχτα, in ancient Greek is an accusative of extent of time. It's found a lot in the LXX. However, I think that the nominative can mean either "this night" or "tonight" and so I was surprised that DL marked "this night" as incorrect. It should be accepted as an alternative rendering. What is your grammatical reasoning for the nominative meaning solely "this night" as opposed to the accusative? ευχαριστώ
I definitely defer to your knowledge of Greek since it is your native language, but in English at least "tonight is gonna last forever" IS a perfectly acceptable alternative to "this night is gonna last forever." Indeed, I would even dare to say that the version with "tonight" is more common in most contexts. The version with "this night" would probably only be said if one were referring not to the night that is approaching the same day when the sentence is uttered but rather to some other specific night- for example: you are looking over your schedule for the week and you see that Tuesday evening you have little planned, so you say to yourself "this night is easy" but then you notice that your mother-in-law is visiting on Wednesday evening, so you say "ugh, this night is gonna last forever."
You're right about "tonight is gonna last forever" being perfectly fine. I neglected that in english "tonight" could be either an adverb or a noun. However, you've just highlighted that "this night" and "tonight" cannot always be used interchangeably and this was exactly my point all along.
Anyway, since this is the greek lesson, the short story is that we use "απόψε" or "αυτή τη νύχτα" for tonight; never "αυτή η νύχτα" as indicated here incorrectly by duo.
Hmm, well, I will start this comment by saying I am not a native speaker of Greek, but based on my understanding, the phrase αυτή το απόγευμα does not make sense- it does as αυτό το απόγευμα but that would mean "this afternoon" (not "her afternoon" which would be το απόγευμα της (just as "her night" would be η νύχτα της)).