They often mean the same, but sometimes they're different.

它們的意思往往是一樣的，但有時又是不同的。

'On time' means 'according to a schedule or a deadline.'

'準時'的意思是'按照時間表或期限'。

If I don't finish my work on time, my boss will be angry.

如果我不按時完成工作，老闆就會生氣。

My train is never on time.

我的火車從來沒有準時過。

'In time' means 'not too late to be successful.'

'及時'的意思是'不晚於成功'。

I missed my deadline, but I still got the presentation finished in time for the meeting.

我錯過了截止日期，但我還是趕在會議前完成了演講。

My train was late but it still arrived in time for me to get to work early.

我的火車雖然晚點了，但還是及時趕到，讓我提前上班。

Neither my presentation nor my train were on time, but they were in time for me to do what I needed to do.

我的演講和我的火車都沒有準時，但它們卻及時地讓我做了我該做的事情。

It's good to be on time.

準時就好。

It's even more important to be in time!

更重要的是要及時!

The difference is down to how flexible your schedule is.

差別就在於你的時間安排是否靈活。

But be careful!

但要小心！

Sometimes if you're not on time, you won't be in time either.

有時候，如果你不按時，你也不會按時。