Mi padre quiere que crucemos la frontera temprano para llegar al sur antes de que se haga de noche.

Because querer que is followed by the subjunctive when one person wants someone else to do something.

• Mi padre quiere cruzar la frontera = My father wants to cross the border.
  Here, my father is the one who wants to do the action himself, so Spanish uses the infinitive cruzar.

• Mi padre quiere que crucemos la frontera = My father wants us to cross the border.
  Here, my father wants us to do it, so Spanish uses que + subjunctive.

And cruzamos would be indicative, not subjunctive, so it does not fit after quiere que.

It is in the subjunctive because the main verb expresses desire/will: Mi padre quiere...

A very common rule in Spanish is:

• verb of wanting / wishing / requesting + que + subjunctive

So:

• quiere que crucemos
• espera que lleguemos
• prefiere que salgamos temprano

The subjunctive here does not mean the action is impossible. It means it is being presented as something desired, not simply stated as a fact.

This is a spelling change that happens in many -zar verbs in forms where z would come before e.

Spanish spelling normally avoids ze and zi, so z changes to c before e.

So:

• infinitive: cruzar
• present subjunctive nosotros: crucemos

Other examples:

• empezar → empecemos
• organizar → organicemos
• rezar → recemos

This is mainly a spelling change, not a big pronunciation change.

Because para + infinitive is used when the subject is the same as the one doing the action in the main clause or when the subject is understood generally from context.

Here, the idea is:

• cross the border early in order to arrive in the south...

The people who cross are also the people who arrive, so Spanish uses:

• para llegar

If the subject changed, para que + subjunctive would be more natural:

• Salimos temprano para que mi padre llegue a tiempo.
  We leave early so that my father arrives on time.

So in your sentence, para llegar is the normal choice.

Al sur means to the south or in the south, depending on context.

In this sentence, llegar al sur means to arrive in the south / reach the south.

Also, al is just the contraction of:

• a + el = al

So:

• llegar al sur = llegar a el sur in theory, but Spanish always contracts it to al sur

Compare:

• Voy al norte = I’m going north / to the north
• Llegamos al sur = We arrived in the south / reached the south

Because antes de que is commonly used when the clause has its own finite verb, and that verb usually goes in the subjunctive when the action is still in the future or not yet completed.

So:

• antes de que se haga de noche = before it gets dark

This is very common because getting dark is seen as a future event relative to the main action.

You can also see:

• antes de salir = before leaving
• antes de que salgamos = before we leave

So the difference is:

• antes de + infinitive when there is no new conjugated verb
• antes de que + subjunctive when there is a full clause with its own verb

Because antes de que normally triggers the subjunctive when the event has not happened yet from the speaker’s point of view.

In the sentence, they want to arrive in the south before night falls / before it gets dark. That is a future, anticipated event, so Spanish uses the subjunctive:

• antes de que se haga de noche

This is similar to:

• antes de que lleguen
• antes de que empiece la película
• antes de que sea tarde

Idiomatic meaning: to get dark / for night to fall

Literally, hacerse often means to become, so:

• hacerse de noche = to become night

Spanish often uses this structure for changes in time/light:

• Se hace de día = It gets light / day breaks
• Se hace tarde = It gets late
• Se hizo de noche = It got dark / night fell

So in your sentence:

• antes de que se haga de noche = before it gets dark

This is a very natural everyday expression.

In hacerse de noche, the verb is part of a fixed pronominal expression. The se is not reflexive in the sense of someone doing something to themselves. Instead, it belongs to the expression meaning to become or to turn into a state.

So:

• hacer = to make / to do
• hacerse = to become / to turn into

Examples:

• Se hizo médico. = He became a doctor.
• Se hace tarde. = It’s getting late.
• Se hizo de noche. = It got dark.

So you should learn hacerse de noche as a whole chunk.

Grammatically, crucemos means we cross in the present subjunctive, so it includes the speaker plus at least one other person.

Whether it includes the father depends on context. It could mean:

• my father wants us all, including him, to cross
• or my father wants us (not necessarily including him) to cross

In real life, context usually makes that clear.

If Spanish wanted to make it obviously about other people, it might use another subject, for example:

• Mi padre quiere que crucéis la frontera... = My father wants you all to cross the border...
• Mi padre quiere que crucen la frontera... = My father wants them/you formal plural to cross the border...

But crucemos by itself simply means we.

Here temprano is functioning like early, and it modifies the idea of crossing the border.

So:

• crucemos la frontera temprano = we cross the border early

This word order is very natural in Spanish. Adverbs like temprano, rápidamente, mañana, etc. often come after the verb phrase.

It helps show that early refers to the crossing, not directly to the father’s wanting.

Compare:

• Mi padre quiere que salgamos temprano. = My father wants us to leave early.
• Mi padre quiere que crucemos la frontera temprano. = My father wants us to cross the border early.

No comma is needed here in normal Spanish punctuation.

The sentence flows as one main idea:

• Mi padre quiere...
• que crucemos...
• para llegar...
• antes de que se haga de noche

Spanish generally does not insert commas before purpose clauses like para llegar or before dependent clauses like antes de que... unless there is a special stylistic reason.

So the sentence is correctly written without commas.

In Spain, especially in central and northern Spain, a learner might notice:

• c before e/i and z are often pronounced like the th in think
• so crucemos and frontera are pronounced a bit differently from many Latin American accents

Approximate pronunciation in Spain:

• Mi padre quiere que crucemos la frontera temprano para llegar al sur antes de que se haga de noche.

A rough guide:

• crucemos ≈ kroo-THE-mos
• frontera ≈ fron-TE-ra
• hacer / haga have a throaty h/j sound: a-KER, A-ga with a stronger back-of-the-throat sound than English h

Also, Spain Spanish often uses a clearer distinction between:

• c/z = th sound
• s = normal s sound

That said, even if you pronounce everything with an s sound, you will still be understood.

Yes, but it means something different.

• Mi padre quiere cruzar la frontera temprano...
  = My father wants to cross the border early...

• Mi padre quiere que crucemos la frontera temprano...
  = My father wants us to cross the border early...

So the difference is about who is supposed to cross:

• quiere + infinitive = same subject
• quiere que + subjunctive = different subject

That is one of the most important contrasts to notice in this sentence.