at [hour] o'clock
at 用于表示具体时刻；o'clock 只用于整点。
The meeting starts at three o'clock.
会议三点钟开始。
……点钟；……点
按照时钟；...点钟；钟头
In conjunction with a numeral, indicates the time within a twelve-hour period (midnight to noon or noon to midnight), specifically the time when the hour hand of a clock points precisely to the symbol or marking corresponding to the designated numeral, i.e., at the hour.
按照时钟
according to the clock
The meeting starts at two o'clock sharp.
会议两点整开始。
用法提示：o'clock 与数字连用，表示整点时间，作时间状语。
AI contextual example
She usually gets up at seven o'clock on weekdays.
她工作日通常七点起床。
用法提示：o'clock 跟在数字后表示“……点钟”，在句中作时刻状语。
AI contextual example
We waited until ten o'clock, but he never came.
我们一直等到十点，但他没有来。
用法提示：o'clock 用于表达具体钟点，强调按钟表计的时间。
AI contextual example
at 用于表示具体时刻；o'clock 只用于整点。
The meeting starts at three o'clock.
会议三点钟开始。
by 表示“不晚于某个时间”。
Please finish the report by five o'clock.
请在五点钟之前完成报告。
between A and B o'clock 中的第二个 o'clock 有时可以省略。
The shop is open between nine and five o'clock.
这家商店在九点到五点之间营业。
grammar · medium
易错句子It's eight thirty o'clock.
正确表达It's eight thirty.
o'clock 只用于整点，如 eight o'clock；表示“几点几分”时不能加 o'clock。
grammar · medium
易错句子The train leaves at fifteen o'clock.
正确表达The train leaves at 3 p.m.
o'clock 只用于 1 到 12 的钟点，不用于 24 小时制；15 点应说 3 p.m. 或 15:00。
grammar · medium
易错句子The class starts at 8 o'clock a.m.
正确表达The class starts at 8 a.m.
o'clock 与 a.m./p.m. 不能并用；需说明上下午时用 8 a.m. 或 eight o'clock in the morning。
在九点钟
The meeting starts at nine o'clock.
会议九点开始。
六点钟之前
Please finish the report by six o'clock.
请在六点钟之前完成报告。
五点整
The train leaves at five o'clock sharp.
火车五点整出发。
大约两点钟
We arrived around two o'clock.
我们大约两点钟到达。
九点新闻
I watched the nine o'clock news.
我看了九点新闻。
（下午或傍晚时脸上冒出的）短胡茬
He showed up with a five o'clock shadow.
他出现时脸上带着短胡茬。
（为白天喝酒找的借口）总有个地方已经到五点了
It's only 10 a.m., but it's five o'clock somewhere.
现在才上午10点，但总有个地方已经到五点了。
现在总有一个地方是五点钟。
Whenever Tom wants a beer before noon, he jokes, 'It's five o'clock somewhere.'
每当汤姆想在中午前喝杯啤酒，他都会开玩笑说：‘现在总有个地方是五点钟。’
现在是十点钟。你知道你的孩子们在哪里吗？
This famous American public-service announcement asked, "It's ten o'clock. Do you know where your children are?"
这条著名的美国公益广告问道：“现在是十点钟。你知道你的孩子们在哪里吗？”
Dictionary facts from DICTIONARY_API_DEV, ECDICT, WIKTIONARY.