Prepositions are always difficult. Here is the example:
The new student usually comes to class on time. or
The new student usually comes to class in time.
Which is right? Both are correct.
Take a look at these:
To be on time: to arrive at the correct time and not be late
The buses here are never on time. They're always late.
We're leaving at 10.00 sharp. So be sure you're on time.
To be in time (for something): to arrive early enough (for something)
I never use an alarm clock but I always wake up in time for the 4 o'clock
news on the radio.
Sorry mom, I won't be home in time for dinner, I have to work late at the office.