"On time" means at the right time, on schedule, at the time it was planned. (准时，按时，正好在计划的时间点，反义是错过计划的时间点)
"in time" means early enough. The opposite of in time is too late. (比计划的时间点更早的一段时间，反义是太迟了)
on time 例句
The plane took off on time.
飞机准时起飞。
I hope the meeting starts on time.
我希望会议准时开始。
I arrive at 4:00 PM, I am on time for the interview.
我下午4点到达，我准时参加面试。
in time 例句
We got to the airport in time to have a coffee before checking in.
我们及时赶到机场，在办理登机手续前喝了杯咖啡。
We'll have to hurry if we want to be in time for the show. 如果我们想赶上演出，就得快点。
I was about to close the door when just in time I remember my key. (at the last moment)
我正要关门，突然我记起了我的钥匙。(在最后一刻)
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