In time = before you are late
On time= punctual
"in time" - there is a deadline. If we are past this deadline, we will miss the chance to do something. The show starts at 8 p.m. and no one is admitted after the show starts. I hope we will make it to the theater in time.
"on time" - there is an expected time. We are meeting friends
for dinner at 7. I hope we will be on time and we don't make them wait for us.