Learn Hardcore Indonesian: Saya terbiasa bangun sebelum matahari terbit.

terbiasa = be accustomed to; emphasizes comfort/familiarity with the action (a state).
biasa (in pattern Saya biasa + verb) = I usually do X; emphasizes habit/frequency.
biasanya = usually (adverb); e.g., Saya biasanya bangun…. All three can be natural, but terbiasa focuses on being used to it, while biasa/biasanya focus on how often it happens.

Does terbiasa mean the English past-habit sense of “used to (but not anymore)”?

No. Terbiasa means “be used to” (a present/general state). For a past habit that you no longer have, use something like Dulu saya biasa/sering bangun sebelum matahari terbit (I used to wake up before sunrise).

Do I need untuk after terbiasa (as in terbiasa untuk bangun)?

No. Saya terbiasa bangun… is perfectly natural. Terbiasa untuk + verb is acceptable but tends to sound more formal or is used before a longer verb phrase (e.g., terbiasa untuk bangun lebih awal demi olahraga).

What’s the nuance between bangun, terbangun, and bangun tidur? And doesn’t bangun also mean “to build”?

bangun = wake up/get up (voluntary/neutral): Saya bangun jam lima.
terbangun = be awakened (often unintentional): Saya terbangun karena suara keras.
bangun tidur = wake up from sleep (explicitly from sleep): Saya bangun tidur lalu mandi. Regarding “build”: the common verb is membangun; bangun shows up in related words (bangunan = building), but for “to build,” use membangun. For “stand up,” use berdiri, not bangun.

Can I use Aku or Gue instead of Saya?

Yes:

Saya = neutral/formal and safe everywhere.
Aku = informal/intimate, common outside formal contexts.
Gue/Gua = very informal Jakarta slang. Match the pronoun to the relationship and setting, and be consistent within a conversation.

Can I omit the subject and just say Terbiasa bangun sebelum matahari terbit?

Yes, in casual speech when the subject is clear from context, you can drop Saya. In a standalone sentence or formal writing, keep Saya.

Can I front the time clause: Sebelum matahari terbit, saya terbiasa bangun?

Yes. That word order is natural. Use a comma after the fronted time clause. Avoid Saya terbiasa sebelum matahari terbit bangun, which is unnatural.

What’s the difference between sebelum and sebelumnya?

sebelum = before (conjunction/preposition) introducing a time/event: sebelum matahari terbit.
sebelumnya = previously/before that (refers back to something mentioned earlier): Sebelumnya, saya tinggal di Bali. You could also see a more formal variant sebelum terbitnya matahari. Synonyms for the time include sebelum fajar, sebelum subuh, or menjelang fajar.

What exactly does terbit mean here? Is it using the ter- prefix?

Terbit means “to rise/appear” (of the sun) and also “to be published.” In this collocation (matahari terbit), it’s a basic intransitive verb meaning “rise.” For sunset, use matahari terbenam.

Does adding sudah change the meaning, as in Saya sudah terbiasa…?

Yes. Saya sudah terbiasa… adds the notion “I’m already used to it (by now).” Without sudah, it’s a neutral statement of being accustomed. Colloquial udah is the informal form of sudah.

How do I say “I’m not used to…”? Should I use tidak or belum?

Saya tidak terbiasa… = I’m not used to it (in general).
Saya belum terbiasa… = I’m not used to it yet (implies that may change). Example: Saya belum terbiasa bangun sedini itu.

How would I include a specific time?

Use jam (everyday) or pukul (more formal): Saya terbiasa bangun sebelum matahari terbit, sekitar jam lima. You can also place the time earlier: Saya biasanya bangun jam lima, sebelum matahari terbit.

Is matahari one word, and should it be capitalized?

Yes, matahari is one word and not capitalized in normal use (it’s a common noun). Capitalize it only at the start of a sentence or if it’s part of a proper name (e.g., the store Matahari).