Saímos daí à noite.

Because Portuguese often drops the subject pronoun when the verb ending already makes the subject clear.

Here, saímos ends in -mos, which tells you the subject is we.

So:

• Saímos daí à noite. = We left / leave from there at night.
• Nós saímos daí à noite. is also possible, but nós is usually added only for emphasis, contrast, or clarity.

It can mean either one.

For the verb sair:

• saímos = we left (preterite / simple past)
• saímos = we leave (present)

The form is identical in both tenses, so you need context to know which one is meant.

For example:

• Ontem saímos daí à noite. → clearly past
• Normalmente saímos daí à noite. → clearly present / habitual

So the sentence by itself is grammatically a bit ambiguous.

The infinitive is sair.

The accent in saímos is important because it shows that a and í are pronounced in separate syllables:

• sa-Í-mos

Without that accent, a learner might try to read it like a diphthong, but that is not how this form works.

So the acute accent on í helps show both:

• the stress
• the separation of vowels

Daí means from there.

It usually refers to a place that is:

• near the person being spoken to, or
• a place that has just been mentioned in the conversation

A useful comparison:

• daqui = from here
• daí = from there (often near you / already mentioned)
• dali = from there over there
• de lá = from there (more general)

So daí is not just any there. It has a slightly more specific pointing function.

Because daí is the normal fused form.

Portuguese commonly combines de with location words:

• de + aqui → daqui
• de + aí → daí
• de + ali → dali

So in normal Portuguese, you would say daí, not de aí.

À noite is the normal expression for at night.

The à is written with a grave accent because it represents a contraction:

• a + a = à

This is part of a fixed time expression, just like:

• à tarde = in the afternoon
• à noite = at night

But compare:

• de manhã = in the morning

Portuguese time expressions are not all built the same way, so this is something you mostly learn as a set phrase.

Because na noite usually refers to a specific night, not the general idea of at night.

Compare:

• Saímos daí à noite. → at night / during the nighttime
• Na noite de sábado, saímos daí. → on Saturday night / on the night of Saturday

So à noite is the natural choice for the sentence you were given.

Yes, de noite also exists, and in many contexts it can be close in meaning to à noite.

But there is often a small nuance:

• à noite = a straightforward time expression, at night
• de noite = often during the night, at nighttime, sometimes with a contrast to daytime

For example:

• Não gosto de conduzir de noite. = I don’t like driving at night.
• Saímos daí à noite. = We left / leave there at night.

In your sentence, à noite sounds very natural and neutral.

It can mean both in Portuguese, but in this sentence to leave is the more natural reading because of daí.

• sair daí = to leave there / get out of there / move away from there

If you were talking about going out socially, Portuguese can also use sair, but the context is usually different:

• Vamos sair à noite. = We’re going out at night / tonight.

So in Saímos daí à noite, the phrase daí strongly points to the idea of leaving a place.

Yes. Portuguese allows some flexibility.

The original order is natural:

• Saímos daí à noite.

But you can also say:

• À noite, saímos daí.

That version puts more emphasis on when it happened.

In general:

• after the verb, daí works naturally as the place/source
• à noite works naturally as the time expression

So the original sentence sounds perfectly normal and neutral.

It is pronounced in two syllables, with the stress on the second one:

• da-Í

In European Portuguese, it sounds approximately like:

• dah-EE, with a reduced first vowel

The accent on í helps show that the second syllable is stressed.