So both "απόψε" and "αυτή η νύχτα" mean "tonight"? Are they used differently or is one more common that the other?
I'd only use "απόψε" to say "tonight" or "this evening" as in "We'll meet tonight." never "αυτή η νύχτα". I think it might be more of the whole night: e.g. ''Μακάρι να τελείωνε αυτή η νύχτα'' "I wish this night was over."
In ancient Greek to indicate through the whole night, the accusative of extent of time was common. It's in Herodotus and the Septuagint. In a different related discussion I asked a native Greek speaker if there's a distinction between nominative αυτή η νύχτα and accusative. English of course doesn't have any temporal distinction based on declensions, since declensions almost completely dropped out long ago. I know it may appear to be splitting hairs, but in an ancient text we can't ask the author what he meant. Does modern Gk still use accusative for time expressions? If so, and if απόψε can mean evening, then it appears we have some subtle distinctions in these phrases in modern Gk, too. Your thoughts are appreciated. Ευχαριστώ