I don't understand the construction of απόψε... There is nothing in there to evoke "nykta" or "spera", which is what I would expect. Where does this word come from and how can I associate it with the night?
I think you just have to learn this word by heart :) to avoid some "useless" extra knowledge... but here's the explanation (of a non linguist!):
Some words of the Ancient Greek language are still used in modern Greek. Even if many "basic" words are not used, their derivatives are still used.
απόψε: ἀπό + ὀψὲ
από (preposition) = by, from, ...
ὀψὲ (Anc.Gr. | adverb) = «αργά», "late".
So «απόψε» is used for "late, during the end of this day", "tonight".
αποψινός (-ή, -ό | adjective) = the one that will happen or has happened tonight, "of tonight"
όψιμος (-η, -ο | adjective) = the one who happens/happened with a delay