If you have a class at 11 am, and you enter the classroom at exactly 11 am, then you are on time for class. On time means punctual. When planes and trains arrive at the scheduled time – not a minute before or a minute after – then, they are on time. Of course, this is something that seldom happens in our country. We Indians are not known for our punctuality – for being on time.
Our physics teacher is always on time for class.
For a change, the flight arrived on time.
When you are in time for a meeting, you arrive a few minutes before the scheduled time – not one or two hours before, but only a few minutes before. If you arrive at 11:13 am for a meeting that is scheduled to start at 11:15 am, then you are in time. If you walk in at 11:16 am, you are late!
I would like all of you to be in time for my talk tomorrow.
I was forced to take a taxi to be in time for the appointment.
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Know Your English 