Learn Hardcore Japanese: zyunbi ga owawattara, hayame ni nemasu. - After the preparations are finished, I will go to bed early.

Here 準備 is the thing that “ends,” so it’s the subject of the intransitive verb 終わる. Intransitive verbs in Japanese take が to mark their subject. If you used the transitive counterpart 終える (“to finish something”), you would say 準備を終えたら instead.

What does the たら in 終わったら mean?

The 〜たら form is a conditional meaning “once/when.” 終わったら literally means “once (I) have finished” or “after (I) finish.” It sets up a condition that, when met, the main clause (going to bed early) will follow.

Could I say 準備を終えたら instead?

Yes. 終える is the transitive verb “to finish (something),” so you would mark its object with を:

準備を終えたら、早めに寝ます。
Both sentences convey “once I finish preparing,” but one uses the intransitive 終わる with が, and the other uses the transitive 終える with を.

Why is there a comma after 終わったら?

In Japanese, commas (読点) often separate clauses or phrases for readability and natural flow. Here the comma clearly marks the end of the conditional clause 準備が終わったら, making the sentence easier to parse.

What’s the difference between 早めに and 早く?

早く means “early/quickly” in a straightforward way.
早めに adds the nuance “a bit earlier than usual” or “in advance.”
So 早めに寝ます implies “I’ll go to bed a bit earlier than normal,” rather than just “I’ll go to bed early.”

Why do we need the に after 早め?

早め is treated like a na-adjective or nominal adjective. To turn it into an adverb that modifies the verb 寝ます, you must add に, yielding 早めに. Without に, the sentence would be ungrammatical.

Why is there no explicit subject like “I” in this sentence?

Japanese often omits the subject when it’s understood from context. Here, the speaker is talking about their own actions, so I is simply implied and not stated.

Is this sentence polite or casual?

It’s polite. The verb 寝ます is in the polite 〜ます form. In casual speech you might hear 早めに寝る instead.