When to use "in time" and when to use "on time"?

When something takes place at the expected or established time, i.e. it is done according to the schedule, we use the word ‘on time’.

in time is used to denote soon enough, i.e. just before the end moment or before the expiry of the set time.

Explanation:

Examples:

We left for the airport on time.

I will reach the restaurant at 12 pm; please be on time.

Joseph set the alarm, to wake up in time, to study for exams.

We are sure that Joseph will finish the work in time.