Menjelang tidur, saya mematikan notifikasi di ponsel.

Menjelang means approaching, toward, or shortly before a point in time.

So menjelang tidur means something like:

• before going to sleep
• as bedtime approaches
• when I’m about to sleep

In this sentence, it sets the time context for the main action.

Both are possible, but they have a slightly different feel.

• sebelum tidur = before sleeping / before bed
• menjelang tidur = as bedtime approaches / shortly before sleep

Menjelang can sound a little more natural when talking about the period leading up to something. It suggests the action happens around that time, not necessarily at a sharply defined moment.

So:

• Sebelum tidur, saya mematikan notifikasi... = perfectly correct
• Menjelang tidur, saya mematikan notifikasi... = also correct, with a slight sense of near bedtime

Because tidur here is being used in a general verbal sense: sleeping / going to sleep.

In Indonesian, time expressions like this often use a bare verb:

• sebelum makan = before eating
• sesudah pulang = after going home
• menjelang tidur = before sleeping

The subject is understood from the main clause, which already has saya. So there is no need to repeat it.

Mati usually means dead, off, or to be off as a state.

Mematikan means to turn off or to switch off something.

So:

• ponselnya mati = the phone is off / dead
• saya mematikan ponsel = I turn off the phone

In your sentence, mematikan notifikasi means to turn off notifications.

This is a common pattern in Indonesian:

• base word: mati
• verb with meN- -kan: mematikan = to cause to be off, so to turn off

Yes, it is natural and understandable.

However, Indonesian speakers may also say:

• menonaktifkan notifikasi = disable notifications
• mematikan notifikasi = turn off notifications

The difference is small in many everyday contexts:

• mematikan sounds very natural in casual use
• menonaktifkan can sound a bit more technical or formal

So this sentence sounds fine.

Indonesian often leaves possession unstated when it is obvious from context.

So di ponsel can naturally mean:

• on the phone
• on my phone

Because the subject is saya, listeners will usually understand that it means the speaker’s phone unless there is a reason to think otherwise.

If you want to be explicit, you can say:

• di ponsel saya = on my phone

Both are correct.

Di is a general location preposition. Depending on context, it can mean:

• in
• on
• at

With devices like phones, Indonesian often uses di where English uses on:

• di ponsel = on the phone
• di komputer = on the computer
• di aplikasi itu = in/on that app

So di ponsel is normal here.

Indonesian nouns usually do not change form for singular vs. plural.

So notifikasi can mean:

• a notification
• notifications

The number is understood from context.

If you really want to emphasize plurality, Indonesian can use reduplication:

• notifikasi-notifikasi

But that is usually unnecessary here. In this sentence, notifikasi naturally means notifications.

Yes. Indonesian is fairly flexible with this kind of time expression.

These are all possible:

• Menjelang tidur, saya mematikan notifikasi di ponsel.
• Saya mematikan notifikasi di ponsel menjelang tidur.

The first version is especially natural because it sets the time first: As bedtime approaches / Before sleeping...

Putting menjelang tidur first slightly highlights the time frame.

The comma separates the introductory time phrase from the main clause.

So:

• Menjelang tidur, = introductory time expression
• saya mematikan notifikasi di ponsel. = main clause

This is similar to English:

• Before going to bed, I turn off notifications on my phone.

In informal writing, people may omit the comma, but using it is good standard punctuation.

Yes, but the nuance is different.

• saya mematikan notifikasi di ponsel = a neutral statement, I turn off notifications on my phone
• saya matikan notifikasi di ponsel = can sound more like I turn off the notifications on my phone with a slightly more direct or definite feel, depending on context

For learners, mematikan is the safer and more straightforward form to use in a plain descriptive sentence.

Yes, ponsel is a common Indonesian word for mobile phone / cellphone.

Other words you may also hear are:

• HP = very common in everyday speech, from handphone
• telepon genggam = more formal, more literal
• smartphone = also used

So these all relate to the same general idea, but ponsel is a good standard choice.

It sounds neutral and natural, leaning slightly standard/formal because of words like:

• saya instead of aku
• ponsel instead of HP
• mematikan instead of a more casual spoken form

A more casual spoken version might be:

• Menjelang tidur, aku matiin notifikasi di HP.

That is more conversational. Your original sentence is a good standard Indonesian sentence for learners to study.