Precisamos mudar o horário da reunião de amanhã.

Because Portuguese often leaves out subject pronouns when the verb ending already makes the subject clear.

• precisamos = we need
• The ending -amos shows the subject is we.

So Precisamos mudar... is completely natural. You could say Nós precisamos mudar..., but nós is usually only added for emphasis, contrast, or clarity.

Precisamos is the 1st person plural (we) form of precisar in the present indicative.

So:

• eu preciso = I need
• você precisa = you need
• nós precisamos = we need

A useful extra note: in Brazilian Portuguese, precisamos can also look identical to the preterite form (we needed) in writing. Context tells you which one it is. In this sentence, it clearly means the present: we need.

In Brazilian Portuguese, when precisar is followed by another verb in the infinitive, the most natural pattern is:

• precisar + infinitive

So:

• Precisamos mudar
• Ela precisa sair
• Eles precisam estudar

With a noun, Portuguese often uses precisar de:

• precisar de ajuda = to need help
• precisar de dinheiro = to need money

In everyday Brazilian Portuguese, people also sometimes drop de before nouns, but with an infinitive, precisar + infinitive is the standard and expected pattern.

After precisamos, Portuguese uses the infinitive to express what needs to be done.

So the structure is:

• precisamos + mudar
• literally: we need + to change

This is very similar to English:

• We need to change...

Portuguese does not need a separate word exactly like English to before the infinitive here. The infinitive itself, mudar, does the job.

Both can refer to time, but they are not always used the same way.

• hora often means the exact clock time: 3 o’clock, what time is it?
• horário often means a scheduled time, time slot, or appointment time

For a meeting, horário is very natural because it refers to the scheduled time of the meeting.

So:

• mudar a hora da reunião = possible
• mudar o horário da reunião = usually more natural when talking about rescheduling

Portuguese uses definite articles more often than English does.

Here, o horário refers to a specific time: the time of that particular meeting. Because it is specific, Portuguese normally includes the article:

• o horário da reunião

Leaving it out would sound unnatural in a normal sentence.

So even though English often says change the meeting time, Portuguese naturally says mudar o horário da reunião.

Da is a contraction of:

• de + a = da

The noun reunião is feminine, so it normally takes the article a:

• a reunião = the meeting

When Portuguese says the time of the meeting, it uses de:

• o horário de a reunião → o horário da reunião

So da reunião literally means of the meeting.

Because reunião is a feminine noun in Portuguese, so it takes:

• a reunião
• da reunião

This is something you simply have to learn with the noun. The ending -ão does not automatically tell you whether a word is masculine or feminine.

For example:

• o avião = masculine
• a reunião = feminine

So it is best to memorize nouns together with their article.

De amanhã describes reunião.

So:

• a reunião de amanhã = tomorrow’s meeting / the meeting tomorrow

Portuguese often uses de + time expression where English uses a possessive or a different structure.

Examples:

• a aula de hoje = today’s class
• o jogo de domingo = Sunday’s game
• a reunião de amanhã = tomorrow’s meeting

It modifies reunião, not horário.

The sentence is best understood in chunks like this:

• [o horário] [da reunião de amanhã]

That means:

• the time
  of
• tomorrow’s meeting

So the sentence is about changing the time of the meeting that will happen tomorrow.

Sometimes yes, but the meaning can change or become less clear.

• Precisamos mudar o horário da reunião de amanhã.
  = We need to change the time of tomorrow’s meeting.

If you say:

• Precisamos mudar o horário da reunião amanhã.

this can sound like tomorrow is when we need to change it, not necessarily that the meeting itself is tomorrow.

So da reunião de amanhã is the clearest way to say tomorrow’s meeting.

Yes. Alterar also means to change, and it can sound a bit more formal than mudar.

• mudar = very common, everyday
• alterar = also common, slightly more formal
• trocar = can mean to switch/exchange, but is less neutral here

For this sentence, mudar is a very natural choice in Brazilian Portuguese.

Not exactly.

• reunião de amanhã = the meeting that is scheduled for tomorrow
• reunião para amanhã = a meeting for tomorrow / planned for tomorrow

In many situations they may point to the same real-world event, but de amanhã is the more direct and idiomatic way to say tomorrow’s meeting in this sentence.

It is completely natural and idiomatic.

A Brazilian speaker would easily say:

• Precisamos mudar o horário da reunião de amanhã.

It sounds like normal everyday Portuguese and is a very useful model for similar sentences, such as:

• Precisamos mudar o local da reunião.
• Precisamos mudar o horário da aula.
• Precisamos remarcar a reunião de amanhã.

The last option, remarcar, is also common when the idea is specifically reschedule.