Learn Hardcore Japanese: osoi zikan ni ie wo deruno ha abunai to omoimasu. - I think leaving the house late at night is dangerous.

In Japanese, you mark a point in time with に. By adding に to 遅い時間 (“late time”), you get 遅い時間に, meaning “at a late hour.” Without に, the sentence would be ungrammatical when you want to say “at” that time.

Why is を used in 家を出る? Doesn’t を only mark direct objects?

Some motion verbs use を to mark the place you pass through or leave. With 出る (“to exit”), 家を出る literally means “to exit the house.” Here the house isn’t a direct object but the location you’re leaving, and を still marks it.

What does the の after 出る do in 家を出るのは?

That の nominalizes the verb phrase 家を出る (“leaving home”) into a noun-like entity. Once nominalized, you can attach は to make that entire idea the topic:
– 家を出るのは… = “As for leaving home…”

Can I replace that の with こと to nominalize?

Yes. You could say 家を出ることは危ないと思います. The meaning stays the same, but:

の is more colloquial and conversational.
こと is more formal or written.

Why is there a と before 思います?

The particle と is the quotative marker. It links your thought or statement to 思います (“think”).
– 危ないと 思います = “I think that it’s dangerous.”
You can’t drop と when using 思う to introduce your opinion.

I don’t see a subject like “I” in the sentence. Is that okay?

Yes. Japanese often omits subjects when they’re clear from context. Here it’s understood you’re saying “I think” or speaking in general, so you don’t need “私は” at the front.

Can I drop 家を and just say 遅い時間に出るのは危ないと思います?

Grammatically yes, but you lose precision. Then it means “Leaving at a late time is dangerous,” and listeners might wonder “leaving where?” If you mean “leaving home,” it’s better to keep 家を.

Could I use 夜遅く家を出るのは危ないと思います instead of 遅い時間に家を出るのは危ないと思います?

Absolutely. 夜遅く (“late at night”) is more idiomatic than 遅い時間に and sounds more natural in spoken Japanese.

Why is the dictionary form 出る used before nominalizing, not the polite 出ます?

When you nominalize with の or こと, you always use the plain (dictionary) form of the verb—in this case 出る—not the -ます form. Polite forms can’t be directly turned into nouns that way.