São nove horas.

Because Portuguese uses the verb ser to tell the time.

• é = singular form
• são = plural form

Since nove horas is plural, the verb is also plural: São nove horas.

Portuguese treats the time as nine hours, so it uses the plural:

• nove horas = literally nine hours
• therefore são = are

So even though English uses singular it’s, Portuguese uses a plural structure here.

Use é when the hour is singular:

• É uma hora. = It’s one o’clock.

Use são for all other numbered hours:

• São duas horas.
• São nove horas.
• São onze horas.

Also note:

• É meio-dia. = It’s noon.
• É meia-noite. = It’s midnight.

Portuguese does not need a dummy subject like English it in expressions like time, weather, or general conditions.

English says:

• It’s nine o’clock.

Portuguese simply says:

• São nove horas.

The verb alone is enough.

Yes. That is very common and completely natural.

• São nove horas. = full form
• São nove. = shorter everyday form

Both are correct. In conversation, people often leave out horas if the meaning is obvious.

You would say:

• Que horas são?

Notice that this also uses the plural são, because horas is plural.

A typical exchange is:

• Que horas são?
• São nove horas.

By itself, São nove horas could mean either 9 in the morning or 9 at night. If you want to be specific, add a time-of-day expression:

• São nove da manhã. = 9 a.m.
• São nove da noite. = 9 p.m.
• São nove da tarde. = 9 in the afternoon/evening, depending on context

These are very common in Brazilian Portuguese.

São has a nasal sound, which is one of the trickier parts for English speakers.

A rough guide:

• s sounds like s
• ão is a nasal diphthong, somewhat like ow but through the nose

So são is roughly like sowng without a clear final g, but nasalized.

The exact Brazilian pronunciation is approximately /sɐ̃w̃/.

Yes, the h in horas is silent.

So horas sounds roughly like:

• OH-ras

In Brazilian Portuguese, the r in the middle is usually a tapped sound, somewhat like the quick tt in American English butter.

So:

• horas ≈ OH-rus / OH-ras, depending on accent

In Brazilian Portuguese, nove is usually pronounced roughly like:

• NOH-vee

The final e often sounds like ee in many Brazilian accents.

So:

• nove ≈ NOH-vee

Not always. São nove horas is correct and natural, but in everyday speech people often shorten it.

Common versions:

• São nove horas.
• São nove.
• Agora são nove. = It’s nine now.

So the full version is fine, but shorter versions are also very common.

You keep são and add the minutes:

• São nove e cinco. = 9:05
• São nove e dez. = 9:10
• São nove e meia. = 9:30
• São nove e quarenta e cinco. = 9:45

Very commonly, Brazilians also say:

• São quinze para as dez. = 9:45

But the nine and forty-five style is very easy and widely understood.

It works in both formal and informal situations.

• In careful or complete speech, São nove horas sounds normal and correct.
• In casual conversation, São nove is often more common.

So the sentence is standard Portuguese, not overly formal.