These two expressions have different meanings - but there's still no need for you to be confused. 'In time' means within sufficient time. For example 'Most tumours can be safely removed if they are diagnosed in time.' Here 'in time' means before it's too late, because if they are not diagnosed within a certain period they may grow too large. 'You could not use 'on time' in this sentence. 'On time' means punctually or at the designated time. For example, 'Am I late? My watch has stopped.' 'No, you're exactly on time. We arranged to meet at 8, and it's 8 o'clock now.'

in time --- to make it to an event without being late ( event is specifed) on time ---- make it to an event without being late ( but the event is not specified) eg Dont worry. I will be there in time for the meeting Dont worry . I will be on time .

I think "in time" means enough to be enough on time! I mean to be early enough

They both mean the same thing. "I want to be on time for the baseball game." "I want to be in time for the baseball game." "We should get there on time for the party." "We should get there in time for the party." They can be used interchangeably. Pretty much whatever you might prefer.