What is the difference between on time and in time?"
"What is the difference between in the end and at the end?"
Michael Swan’s excellent Practical English Usage (Oxford University Press), provides a succinct answer to both of these questions:
"On time = at the planned time; neither late nor early:
file:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/spacer.giffile:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/structure-common-bullet-bar-green.giffile:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/spacer.gifPeter wants the meeting to start exactly on time.
In time = with enough time to spare; before the last moment:
file:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/spacer.giffile:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/structure-common-bullet-bar-green.giffile:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/spacer.gifHe would have died if they hadn’t got him to the hospital in time."
"In the end = finally, after a long time:
file:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/spacer.giffile:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/structure-common-bullet-bar-green.giffile:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/spacer.gifIn the end, I got a visa for Russia.
At the end = at the point where something stops:
file:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/spacer.giffile:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/structure-common-bullet-bar-green.giffile:///C:/Documents%20and%20Settings/Administrator/Desktop/Prepositions%20-%20in%20time%20v%20on%20time%20-%20grammar%20-%20central%20-%20British%20Council%20-%20LearnEnglish_files/spacer.gifI think the film’s a bit weak at the end.

great effort and God bless you

On time = at the planned time; neither late nor early

Peter wants the meeting to start exactly on time.

In time = with enough time to spare; before the last moment

He would have died if they hadn’t got him to the hospital in time

In the end = finally, after a long time

In the end, I got a visa for Russia

At the end = at the point where something stops

I think the film’s a bit weak at the end