Learn Hardcore Japanese: watasi ha benkyou no zikan ni koohii wo nomimasu.

In Japanese, は marks the topic of the sentence (“as for me”), not necessarily the grammatical subject. By saying 私は, you’re setting up “I” as what you’re talking about (topic), then commenting that during study time you drink coffee. If you used が (私が), you’d be marking “I” as the subject in a more neutral or new-information context, which can feel unnatural here since you’re speaking about your habitual action.

What is the role of の in 勉強の時間?

The particle の links two nouns in a possessive or descriptive way. In 勉強の時間, it literally means “the time of studying,” i.e. “study time.” You can think of it as turning 勉強 (studying) into an adjective that describes what kind of 時間 (time) it is.

Why is に used after 時間? Could we use で instead?

When you talk about a specific point or period in time and say “at” or “during” that time, you use に. So 時間に means “at that time” or “during that period.”
Using で (the location/means marker) would be incorrect here because you’re not describing a place or instrument but a time frame.

Why is コーヒー followed by を?

The particle を marks a direct object—the thing that the verb acts upon. Here, コーヒーを飲みます means “drink coffee,” so コーヒー (coffee) is what you’re drinking, and を flags it as the object of 飲みます.

Why is the verb 飲みます placed at the end of the sentence?

Japanese follows a Subject–Object–Verb (SOV) order. You first introduce the topic/subject (私は), then other elements (time, object), and finally the verb (飲みます). This verb-final structure is standard and what gives Japanese its characteristic rhythm.

Can we omit 私 in this sentence? When are pronouns dropped in Japanese?

Yes. If the context makes it clear who you’re talking about, you can drop 私 and simply say 勉強の時間にコーヒーを飲みます. Japanese often omits pronouns when they’re obvious — especially in casual conversation or when you’ve already mentioned the person.

What is the difference between 飲みます and 飲む?

飲みます is the polite (masu-form) present tense of “to drink,” used in formal or respectful contexts. 飲む is the plain/dictionary form, used in casual speech, writing, or when listing verbs.
Example casual: 勉強の時間にコーヒーを飲む。

How could I say “while studying” more directly, using 〜中?

You can replace 勉強の時間に with 勉強中に.
So the sentence becomes:
私は勉強中にコーヒーを飲みます。
Here, 中 (ちゅう) means “in the middle of,” so 勉強中 = “while studying.”