On Time vs In Time

These expressions are very similar, but there is a slight difference in meaning.

On time
On time means that there is a specific time established when something is supposed/expected to happen, and it is happening at the planned time.
I want to start the meeting on time so please don’t be late.
The 11.45 train left on time.

In time
If we say we arrived in time, we’re saying that we got there a little early – that there was time to spare.
We often use the structure in time to do something:
We arrived in time to get some drinks before the show started.
Will you be home in time for dinner?

taken from:

http://languagelearningbase.com/88875/difference-between-in-time-and-on-time