in time and on time are completely different from each other.
when I arrive somewhere on time, that means that i was sopposed to be there at 8.00 and i was there at about 7.50 . means a little sooner that the appointed time
but when i was supposed to be somewhere at 8.00 and i get there exactly at 8.00 or 7.59 or the time about a minute sooner or later , i get there IN TIME.
Hope that helps.ask me if you are not satisfied yet.