Когда мы вышли из театра, было уже за полночь.

Вышли is the perfective past form of выйти, so it presents the action as completed: we went out / we came out.

In this sentence, the speaker is referring to the moment after they had exited the theater, so a completed action fits naturally.

If you used выходили instead, it would sound more like:

• a repeated action,
• an ongoing process,
• or background description in the past.

So here Когда мы вышли из театра... means When we came out of the theater..., focusing on the finished event.

Because the subject is мы (we), and in the past tense Russian verbs agree in number and sometimes gender.

Past tense endings:

• masculine singular: no extra ending, e.g. вышел
• feminine singular: вышла
• neuter singular: вышло
• plural: вышли

Since мы is plural, the verb must be вышли.

The preposition из (out of / from inside) requires the genitive case.

So:

• театр = nominative
• театра = genitive singular

That is why you get из театра = out of the theater.

This is a very common pattern:

• из дома = out of the house
• из школы = out of school
• из магазина = out of the store

Because из is used when someone moves out from inside a place.

They were inside the theater, and then they came out, so:

• выйти из театра = to come out of the theater

Compare:

• из = from inside
• с = from the surface of something, or from an event in some cases
• от = away from a person or from near a place

So из театра is exactly what Russian expects here.

Because this is an impersonal time expression.

Russian often uses было in sentences about time, weather, or general conditions, where English uses it was:

• Было поздно. = It was late.
• Было холодно. = It was cold.
• Было около часа. = It was about one o’clock.

So было уже за полночь literally works like it was already past midnight.

If you said была полночь, that would mean it was midnight, treating полночь as the grammatical subject. But here the idea is not it was midnight, but it was already past midnight, so the impersonal structure with было is natural.

За полночь is an idiomatic expression meaning past midnight or after midnight.

It does not literally mean something like behind midnight in normal English. In time expressions, за can have special idiomatic uses.

So:

• было за полночь = it was past midnight
• уже за полночь = it was already past midnight

This is a fixed, common way to talk about late time.

Уже means already.

It adds the sense that by that point, the time had already passed midnight. It gives a nuance of surprise, lateness, or emphasis on how late it was.

Compare:

• было за полночь = it was past midnight
• было уже за полночь = it was already past midnight

So уже makes the statement feel a bit more pointed.

Because Russian often leaves out the kind of dummy subject that English requires.

English says:

• It was late
• It was cold
• It was past midnight

Russian usually just says:

• Было поздно
• Было холодно
• Было за полночь

So there is no actual Russian word here corresponding to English it.

Because Когда мы вышли из театра is a subordinate clause introduced by когда (when).

In Russian, subordinate clauses are normally separated by commas:

• Когда мы вышли из театра, было уже за полночь.

This is true whether the subordinate clause comes first or second:

• Когда мы вышли из театра, было уже за полночь.
• Было уже за полночь, когда мы вышли из театра.

Here it means when, referring to a specific point in time.

Because вышли is perfective and completed, the clause points to the moment of exiting:

• Когда мы вышли из театра... = When we came out of the theater...

If the verb were imperfective, the sense could shift more toward while or an ongoing situation, depending on context.

Yes. Russian word order is flexible, although different orders can change emphasis.

The given version is very natural:

• Когда мы вышли из театра, было уже за полночь.

You could also say:

• Было уже за полночь, когда мы вышли из театра.

Both mean essentially the same thing, but the focus shifts:

• starting with Когда мы вышли... emphasizes the event first,
• starting with Было уже за полночь... emphasizes how late it was.

Yes, but it is not exactly the same stylistically.

• После полуночи = after midnight
• За полночь = past midnight

После полуночи is more neutral and straightforward. За полночь is a very natural idiomatic time expression and often sounds a bit more vivid in this kind of sentence.

So:

• было уже после полуночи = it was already after midnight
• было уже за полночь = it was already past midnight

Both are correct, but the original sounds especially natural in narrative Russian.