I was reading a text-block in my book regarding the difference between in time and on time, and I noticed before in time, the writer (of the book) put just in 2 different examples.
Here are the sentences:
We arrived just in time to hear the Prime Minister's speech.
Our plane was on time and she was waiting for us at the airport.
We got there just in time for dinner.
I expect she will be late – the trains are never on time.
I've looked up the just in my dictionary and it collocates with in time; just in that sentence means exactly. We also know the definition of on time is punctual or neither early nor late. Is it correct to put it just before it? I wonder whether it changes the meaning of the phrase (on time).
Some people here said they are interchangeable, just in time and just on time are, if I'm not mistakenly understood.
Best Answer
"Just in time" is a very common phrase, perhaps even a set phrase. It means having achieved a deadline but with no margin to spare. Yes it means "exactly on time" but it implies a situation in which one is on the edge of failure.
In business "just in time delivery" means a model in which goods or parts are delivers the same day, perhaps even the same hour that they are needed. This will bring a failure if there is any delay in the earlier part of the logistic chain, but in many cases achieve a measure of savings.
"Just on time" is not a usual phrase. I would hesitate to say just how it changes the meaning of "on time", and I would advise avoiding it as likely to be unclear or surprising to listeners or readers.