The meaning of "the day after" and "the night before"

Question

When we say "the night before" do we mean a particular night that took place before some event or some period of time that lasted until last night?

"Treat me like you did the night before" (song by the Beatles)

In this song it is clear that the author wants his lady to treat him the same way she had been treating him until last night, so the meaning is "the time that lasted until last night".

However, when I consider the name of the movie "The Day After" - that famous one about the Third World War - I find it more likely to mean "the day after the event/happening" rather than "a period of time that starts right after the day is over". In that movie all the nuclear explosions happened in the evening, and the movie is showing us what's happening on the very next day, that is, on "the day after the terrible disaster".

So, now I am confused.

To sum up,

Does "the night before" mean "the time that lasted until last night" or "the night that took place before some event"?

Does "the day after" mean "the time that starts when the day is over" or "the day that takes place after some event"?

Answer 1

In casual speech, you can leave out the word after before or after as long as you provided enough context with previous sentences or clauses.

For example:

I thought the event was on the 30th, but it turns out it was the night before. (before the 30th)

On that day, his eyes were red. The day after, they were fine. (after that day)

Generally, those types of phrases do not refer to "the night before today," but it is grammatically valid. That Beatles song could be using it that way, but out of context it doesn't mean too much. At least that's my take.