Learn Hardcore Japanese: eiga ha yoru ni hazimarimasu.

Using 映画は夜に始まります frames the sentence around the topic “the movie” and then tells us when it starts.
If you said 映画が夜に始まります, you’d simply state the fact “the movie starts at night,” with no topical nuance or implied contrast.

Why is 夜 followed by the particle に?

に marks 夜 as a specific point in time (“at night”). In Japanese:

に attaches to precise time words (hours, days, “night,” etc.).
夜に means “at night.”
Without に, the sentence would sound unnatural when referring to that specific time.

Could we omit the に and just say 映画は夜始まります?

No. For words like 夜, に is required to mark the time. Omitting に here makes the sentence ungrammatical.
Note, however, that some time expressions (今夜, 毎日, 明朝) don’t need に, but plain 夜 does.

Why doesn’t 映画 take を as in “direct object”?

Because 始まる is an intransitive verb (“to begin” by itself). Intransitive verbs do not take a direct object.

Transitive: 始める (“to start something,” takes を)
Intransitive: 始まる (“something starts,” no を)

What’s the difference between 始まる and 始める?

始まる is intransitive:
・The action happens on its own (“The movie begins”).
始める is transitive:
・Someone actively starts something (“We start the movie”).

Why does the verb 始まります come at the end of the sentence?

Japanese follows a Subject/Topic – Time – Object – Verb (S/T/O/V) order. The verb always goes last, summarizing the action after all context (topic, time, place, object) has been introduced.

What does the ます ending on 始まります indicate?

The -ます form is the polite present tense.

Dictionary (plain) form: 始まる (“begins”)
Polite form: 始まります (“begins,” said politely)

Is there an explicit subject in this sentence?

No, Japanese often omits subjects when they’re clear from context. Here, we understand that “the movie” (or the schedule/theater) is what’s starting; no extra pronoun or noun is needed.