Фотофиксацию сделали ночью.

Because it is the direct object of the verb сделали.

• Dictionary form: фотофиксация
• In the sentence, it answers what did they do/make?
• Feminine nouns ending in -я usually change to -ю in the accusative singular

So:

• фотофиксация = nominative
• фотофиксацию = accusative

That is why the sentence has Фотофиксацию сделали ночью.

It is a fairly formal or technical word meaning something like:

• photographic recording
• photo documentation
• photographic evidence collection
• recording something by taking photos

It is not the most everyday conversational word. In official, legal, technical, or police-style language, it can refer to documenting something with photographs.

This is a very common Russian pattern. Russian often uses a 3rd person plural verb with no stated subject to mean:

• they did it
• someone did it
• it was done (without using a true passive)

So сделали here does not necessarily mean a specific they. It often just means that some unnamed people carried out the action.

In natural English, this may be translated more passively:

• The photo documentation was done at night.

Yes. A more explicitly passive version would be:

• Фотофиксация была сделана ночью.

That also means The photo documentation was done at night.

The difference is mostly stylistic:

• Фотофиксацию сделали ночью = indefinite they did it
• Фотофиксация была сделана ночью = more direct passive, often more formal/bookish

Both are grammatical and natural in the right context.

Because сделали is perfective, and it presents the action as completed.

• делали = were doing / did (process, repeated, or ongoing)
• сделали = did, completed, finished

Here the idea is that the photo documentation was carried out and completed at night, so сделали fits well.

If you said делали ночью, it would sound more like:

• they were doing it at night
• they used to do it at night
• they did it at night repeatedly

Ночью is the normal adverbial form meaning at night or during the night.

Historically and grammatically, this is the instrumental case of ночь, used adverbially.

So:

• ночь = night
• ночью = at night / during the night

This is very common with time expressions in Russian, for example:

• утром = in the morning
• днём = during the day
• вечером = in the evening
• ночью = at night

By itself, ночью usually means:

• at night
• during the night

It does not automatically mean last night.

If you want last night, Russian more often says:

• прошлой ночью

So in this sentence, ночью simply tells you the action took place at night.

Russian word order is flexible, so the sentence could be rearranged:

• Фотофиксацию сделали ночью.
• Ночью сделали фотофиксацию.
• Сделали фотофиксацию ночью.

These all mean roughly the same thing, but the emphasis changes.

The given order puts фотофиксацию first, which may suggest that this is the topic already under discussion: as for the photo documentation, it was done at night.

Yes, it sounds fairly formal, official, or technical, mainly because of the noun фотофиксация.

A more everyday sentence might use something simpler, depending on context, such as:

• Фотографии сделали ночью. = The photos were taken at night.
• Снимки сделали ночью. = The shots/photos were taken at night.

So the original sentence sounds like something from a report, inspection, police record, technical description, or legal context.

It is feminine.

You can tell because it ends in -я in its dictionary form:

• фотофиксация

That is also why, in the passive version, you would say:

• Фотофиксация была сделана ночью.

Both была and сделана agree with the feminine noun.

A rough pronunciation guide is:

• Фотофиксацию сделали ночью
• fotafiksAtsiyu sdElali nOch'yu

A few helpful notes:

• фото- sounds like fo-to
• -кса- in фиксацию is pronounced clearly
• сделали begins with a consonant cluster: zdye- or s-dye- depending on how carefully you say it
• ночью has a soft ч sound, roughly NO-chyu

Grammatically, yes, сделали comes from сделать, often translated as to do or to make. But in English, a literal made photo documentation sounds unnatural.

In this sentence, better translations are:

• carried out
• did
• completed
• was done

So learners should understand the Russian verb literally, but translate the whole sentence naturally rather than word-for-word.