Learn Hardcore Portuguese (Brazil): Quanto tempo você precisa para sair de casa, dez ou vinte minutos? - How much time do you need to leave the house, ten or twenty minutes?

You would not normally use something like quão longo in this context. Quão is much rarer and tends to be used in more literary or specific structures, not for asking about time like this.

Why is it tempo (singular) and not tempos, like “quantos tempos”?

When tempo means “time” as a general quantity or duration, it behaves like an uncountable noun in Portuguese, so it stays in the singular:

Quanto tempo falta? – How much time is left?
Não tenho tempo. – I don’t have (any) time.

You would almost never say quantos tempos to mean “how many units of time”; that sounds wrong in this sense. Tempo only normally goes to plural (tempos) in other meanings, like:

naqueles tempos – in those days
os tempos mudaram – times have changed

But for “how much time”, always use quanto tempo (singular).

I learned that precisar is usually precisar de (“to need”). Why is there no de here, and can I say De quanto tempo você precisa… instead?

You will see both patterns with precisar in Brazilian Portuguese:

precisar de + noun (very standard)
- Preciso de dinheiro. – I need money.
- Ela precisa de ajuda. – She needs help.
precisar + noun (also common in everyday Brazilian speech, though some grammars are stricter about it)
- Preciso um favor seu. (colloquial, some would correct to Preciso de um favor seu.)

In your sentence:

Quanto tempo você precisa…
Here, quanto tempo is the direct object of precisa.

Many Brazilians say this exactly as written, and it sounds natural and common. More “textbook” or formal versions are:

De quanto tempo você precisa para sair de casa?
Você precisa de quanto tempo para sair de casa?

All three are used in Brazil:

Quanto tempo você precisa…? – Very natural in speech.
De quanto tempo você precisa…? – Also natural; slightly more careful/formal.
Você precisa de quanto tempo…? – Same meaning, but emphasizes the amount of time (like “So how much time is it that you need?”).

For practical purposes, you can treat all of them as correct in Brazilian Portuguese.

Why is it para sair and not por sair or something else?

Para + infinitive is the normal way to express purpose or goal in Portuguese:

para sair de casa – in order to leave the house / to leave the house
para estudar – to study / in order to study
para chegar na hora – to arrive on time

Using por here would be wrong, because por usually expresses ideas like cause, motive, exchange, route, etc., not purpose in this sense:

Ele ficou em casa por estar doente. – He stayed home because he was sick.
Paguei pouco por este livro. – I paid little for this book.

So in your sentence, para sair de casa = in order to leave home, which is exactly the idea of purpose.

What exactly does sair de casa mean? Is it just “to leave the house”? Is it different from ir embora de casa or sair da casa?

Sair de casa literally is “to go out from home / to leave home”, but it’s often used the way English speakers say “to leave the house” or “to head out” in daily life.

Vou sair de casa às oito. – I’ll leave home at eight.

Some contrasts:

sair de casa – neutral, everyday: leave home / leave the house (usually yours).
ir embora de casa – to move out (for good or for a long time), leave home in the sense of no longer living there:
- Ele foi embora de casa aos 18 anos. – He moved out (left home) at 18.
sair da casa – more literally “leave the house”, a specific house with an article:
- Ele saiu da casa correndo. – He ran out of the house.
  This can be any house, and it focuses more on the physical building, not so much on “home” as an idea.

In your sentence, sair de casa is just about the normal act of getting ready and going out from where you live.

Why is it de casa and not da casa?

When casa means “home” (your home) in a generic sense, Portuguese often drops the article and uses fixed combinations with prepositions:

em casa – at home
de casa – from home
para casa – home / to home

So:

Vou sair de casa. – I’m going to leave home.
Cheguei em casa. – I arrived home.

If you say da casa ( = de + a casa), you are now talking about “the house” as a specific building:

Ele saiu da casa do vizinho. – He left the neighbor’s house.
O gato entrou na casa e depois saiu da casa. – The cat went into the house and then left the house.

In your sentence, the idea is your general home, so de casa is the natural choice.

Can I omit você here? Could I use tu instead?

Yes, there is some flexibility:

Omitting “você”
- Quanto tempo você precisa para sair de casa…? – Very natural.
- Quanto tempo precisa para sair de casa…? – Also grammatical, but:
  - sounds more formal or impersonal, like “How long does one need…?”
  - or could be understood as a generic question, not to a specific “you”.

In everyday Brazilian conversation, people usually keep você here.

Using “tu”
In many regions (especially the South and some parts of the Northeast), people say tu instead of você, often with 3rd‑person verbs:

Quanto tempo tu precisa pra sair de casa? (common colloquial pattern)

More “textbook” agreement would be:

Quanto tempo tu precisas para sair de casa?

So yes, you can replace você with tu, depending on regional usage, but keep in mind the local verb agreement patterns.

Can I change the word order, like Você precisa de quanto tempo para sair de casa?

Yes. Word order is flexible, and different orders slightly change the emphasis, not the basic meaning.

Some options:

Quanto tempo você precisa para sair de casa?
– Neutral, very common: “How much time do you need…?”
De quanto tempo você precisa para sair de casa?
– Slightly more formal / careful; still very natural.
Você precisa de quanto tempo para sair de casa?
– Puts extra emphasis on “how much time”, often used when clarifying or surprised:
– Like: “So how much time is it that you need to leave the house?”

All three are acceptable in Brazilian Portuguese.

What is the function of the comma before “dez ou vinte minutos?”

The comma separates the main question from a follow‑up with options:

Quanto tempo você precisa para sair de casa, dez ou vinte minutos?

This is like in English:

“How long do you need to leave the house, ten or twenty minutes?”

The structure is:

General question: Quanto tempo você precisa para sair de casa – How much time do you need…
Then, immediately proposing two possible answers: dez ou vinte minutos? – ten or twenty minutes?

You could also write it as two sentences:

Quanto tempo você precisa para sair de casa? Dez ou vinte minutos?

Both ways are common in writing; in speech, you’d normally make a brief pause before “dez ou vinte minutos”, which the comma represents.

Could I also say Quanto tempo você leva para sair de casa, dez ou vinte minutos?? What’s the difference between precisar and levar here?

Yes, you can say:

Quanto tempo você leva para sair de casa, dez ou vinte minutos?

It’s very natural. The difference is:

precisar – focuses on how much time you need / require (subjective need, preparation, etc.).
levar (time) – focuses on how long it actually takes you in practice.

In many situations, they’re almost interchangeable:

Quanto tempo você precisa para sair de casa?
Quanto tempo você leva para sair de casa?

Both can be understood as “How long does it take you to get ready and leave the house?”.

In real speech, would Brazilians say para or more often pra here? Is pra correct in writing?

In everyday Brazilian speech, pra is extremely common:

Quanto tempo você precisa pra sair de casa…?

pra is a contracted, informal form of para (and sometimes para a). Usage:

Speech: pra is by far more frequent in casual conversation.
Informal writing (messages, chats, social media): pra is totally fine and very common.
Formal writing (essays, official documents, academic texts): prefer para.

So you can think:

para – more neutral / formal.
pra – very colloquial and widely used, especially in Brazil.

Is there any difference between Quanto tempo você precisa para sair de casa? and Por quanto tempo você precisa sair de casa?

Yes, they mean quite different things:

Quanto tempo você precisa para sair de casa?
– How much time do you need in order to leave home?
– Focus: the preparation time before you leave (get dressed, pack your things, etc.).
Por quanto tempo você precisa sair de casa?
– For how long do you need to be away from home?
– Focus: the duration of your absence from home (how long you will stay out).

So:

Use quanto tempo você precisa para… when you mean how much time do you need before doing X.
Use por quanto tempo when you mean for how long (a duration) will something last.