Cóng bā diǎn dào jiǔ diǎn wǒ zài túshūguǎn xuéxí.

Chinese often fronts time expressions as the topic for emphasis. You have several natural options:

• 从八点到九点，我在图书馆学习。 (Fronted time = stronger emphasis on the time range)
• 我从八点到九点在图书馆学习。 (Very common: Subject + time + place + verb)
• 我在图书馆从八点到九点学习。 (Also possible; slightly stronger emphasis on the place first)

All are grammatical; you choose based on what you want to highlight (time vs. place).

You can drop 从 in speech and writing: 八点到九点我在图书馆学习 is natural. Keeping 从 is also fine. For learners, two safe patterns are:

• With 从: 从八点到九点我在图书馆学习。
• Without 从: 八点到九点我在图书馆学习。

Here 在 introduces location: 在图书馆 = “at the library.” To mark the progressive “be doing,” you can put 在/正在 before the verb:

• Location only: 我在图书馆学习。
• Progressive (general): 我在学习。
• Progressive at a place: 我正在图书馆学习。 (Clear and natural) Avoid doubling 在 (e.g., 我在图书馆在学习)—use 正在 instead.

Chinese doesn’t require tense marking. A past time word is often enough:

• 昨天从八点到九点我在图书馆学习。 (already clearly past) You can add perfective 了 for a completed-event feel:
• 昨天从八点到九点我在图书馆学习了。 Both are acceptable; 了 highlights completion rather than “pastness.”

Use a duration phrase with 一个小时:

• Neutral/habitual/scheduled: 我在图书馆学习一个小时。
• Completed once: 我在图书馆学习了一个小时。 Note: With a duration, 了 after the verb commonly marks a completed event.

A common template is: Subject + Time + Place + Verb (+ Object).

• 我（昨天）从八点到九点在图书馆学习。 You can front time or place for emphasis, but this base order is a safe default.

Use part-of-day words before the time:

• Morning: 早上/上午八点
• Afternoon: 下午两点
• Evening: 晚上九点 For ranges: 从晚上八点到九点.

Yes. Use 到 as “until” with the verb:

• 我在图书馆学到九点。 (studied/study until nine) If you also want the start time, add 从: 我从八点学到九点 (often understood to be at the same place if context is clear).

至 is a more formal/literary counterpart to 到 in ranges:

• 从八点至九点 (formal, you’ll see it in notices/schedules) In everyday speech, 到 is more common.

Yes, if the subject is obvious from context (e.g., in a schedule or when answering a question):

• 从八点到九点在图书馆学习。 In a standalone sentence, keeping 我 is clearer.

Use 去 for motion:

• 我从八点到九点去图书馆学习。 (focus on going there to study) Your original sentence 我在图书馆学习 emphasizes being at that location during that time.

Optional. With a long fronted adverbial, a comma can improve readability:

• 从八点到九点，我在图书馆学习。 Without the comma is also fine in simple sentences.