IN Months Cities and countries
Seasons Rooms and buildings
Periods of the day
(exception: at night)
(exception: in a car)
in time / on time
If I arrive at 4:00 PM, I am on time for the interview.
If it leaves at 10:30 AM, the flight is leaving on time.
If it does start at 9:00 with no delays, it is starting on time.
If you say “He’s always on time” it means he is punctual; he always arrives at the correct time, he is not late.
If you say “He’s never on time” it means he is always late.
In time means that something happened at the last moment before it was too late; before something bad would happen.
We often say “just in time” to emphasize that something happened immediately before the limit/deadline, as you can see by comparing the last two example sentences.
There’s also the expression “in the nick of time” which even further emphasizes something happening at the last moment, immediately before the limit/deadline: