Besok pagi saya harus piket di ruang kelas sebelum guru datang.

Yes, besok by itself means tomorrow. Adding pagi makes the time more specific:

• besok = tomorrow
• pagi = morning
• besok pagi = tomorrow morning

This is very natural in Indonesian. Time expressions are often built by simply putting the words together without extra prepositions like in or on.

Examples:

• besok malam = tomorrow night
• besok siang = tomorrow afternoon / midday
• besok sore = tomorrow late afternoon

Indonesian often puts time expressions near the beginning of a sentence, especially when setting the scene.

So:

• Besok pagi saya harus piket... = Tomorrow morning I have to be on duty...

This is very normal, but other word orders can also work depending on emphasis. For example:

• Saya harus piket besok pagi...

That also makes sense, but starting with besok pagi sounds very natural when you want to frame the sentence by time first.

Harus means must, have to, or need to.

In this sentence, it shows obligation:

• saya harus piket = I have to do duty / I must be on duty

A few related words:

• harus = must, have to
• perlu = need to
• boleh = may, allowed to
• bisa = can, able to

So harus is stronger than simply saying something is needed; it usually means there is some rule, duty, or expectation.

Piket refers to being assigned duty, especially in places like schools, offices, or organizations. In many school contexts, it means doing routine responsibilities such as cleaning, preparing the room, or being responsible for the classroom.

In harus piket, piket functions very naturally like a verb in everyday Indonesian, even though the word is closely tied to the idea of duty/shift/assigned duty.

So:

• Saya harus piket = I have to do duty / I’m assigned to duty

Common school-related use:

• anak piket = the student(s) on duty
• jadwal piket = duty schedule
• piket kelas = classroom duty

Indonesian often does not need a separate verb like be in places where English does.

Here:

• di ruang kelas = in the classroom

So the sentence does not need something like be in. Indonesian can simply say:

• saya harus piket di ruang kelas

Literally, this is something like:

• I must do duty in the classroom

This is normal Indonesian structure.

Di is a preposition here, meaning in, at, or on, depending on context.

• di ruang kelas = in the classroom

Important: this di is separate from the following word because it is a preposition.

Compare:

• di ruang kelas = in the classroom
• datang = come
• ditulis = written

When di- is a prefix used in passive verbs, it is written together with the verb:

• ditulis = written
• dibaca = read

When di shows location, it is written separately:

• di sekolah = at school
• di rumah = at home

Both can be used, but they are slightly different in nuance.

• kelas can mean class or classroom, depending on context.
• ruang kelas more explicitly means classroom as a physical room.

So:

• di kelas = in class / in the classroom
• di ruang kelas = in the classroom

Using ruang kelas makes the location more concrete and specific as a room. Using kelas alone would also be very common in everyday speech.

Indonesian does not have articles like a, an, or the.

So:

• guru can mean teacher or the teacher
• ruang kelas can mean a classroom or the classroom

The exact meaning depends on context.

In this sentence, the context makes it natural to understand:

• guru = the teacher
• ruang kelas = the classroom

This is one of the big differences from English.

Sebelum guru datang is already a complete and natural clause meaning before the teacher comes/arrives.

Breakdown:

• sebelum = before
• guru = teacher / the teacher
• datang = come, arrive

Indonesian often uses a simple clause after words like sebelum:

• sebelum guru datang = before the teacher comes
• setelah saya makan = after I eat
• ketika dia tidur = when he/she sleeps

You do not need an extra ending like -nya here.

Adding itu would mean that teacher or the teacher with stronger specificity:

• sebelum guru itu datang = before that/the teacher comes

That is possible, but the original sentence sounds more natural unless there is a special need to identify the teacher more clearly.

It can be translated as either come or arrive, depending on natural English.

• datang literally often means come
• in many contexts, especially with places or events, English may prefer arrive

So:

• sebelum guru datang can be understood as
  • before the teacher comes
  • before the teacher arrives

Both are fine. In natural English for this sentence, arrives may sound slightly more natural.

Indonesian often leaves out information that is already clear or unnecessary.

In this sentence:

• di ruang kelas already gives the location of the duty
• guru datang is enough to mean the teacher comes/arrives there, in the understood situation

You certainly could say:

• sebelum guru datang ke ruang kelas = before the teacher comes to the classroom

That is grammatical, but it is more explicit than necessary. The original version is shorter and more natural.

Yes, in some contexts Indonesian can omit saya if the subject is already obvious.

For example, in conversation:

• Besok pagi harus piket di ruang kelas sebelum guru datang.

This could still be understood as I have to be on duty... if the context makes that clear.

However, including saya is safer and clearer, especially for learners and in standalone sentences.

It is neutral and natural, and it fits well in everyday standard Indonesian.

A few notes:

• saya is polite/standard for I
• harus is standard
• piket is very common in school and workplace contexts
• guru is standard for teacher

In casual conversation, someone might say:

• Besok pagi aku harus piket di kelas sebelum guru datang.

That sounds more informal because of aku and di kelas.

So the original sentence is not stiffly formal, but it is more on the standard/polite side.