"In time" is to do something before you run out of time, but "on time" is typically used when you do something at the designated time. For example, if you have a job interview at 12:00 PM and you get there at 11:59 AM, then you barely made it on time. If you get to the interview at 11:45 AM however, then you made it in plenty of time. Having said this, native speakers use "in time" and "on time" interchangeably :-)

One of the things that we need to understand about prepositions is that they create a relation with the noun or verb that comes before them in a sentence, and their object. Sometimes these relations are about real pysical relations and sometimes they are about more abstract relations. IN - This preposition creates a relation about boundaries. Notice how all the objects after the preposition have a boundary that contains either the action or the thing (noun) that comes before the preposition. Physical relation: The boy put his toys in the box. - the boundary of the box/ toys (noun) in the box We met in the lobby. - the boundary of the lobby - the action (meet) in the lobby I like raisins in my pudding. - the boundary of the pudding - the raisins (noun) in the pudding Abstract reation: I will keep this idea in mind. - the abstract boundary of the mind - idea (noun) in mind. I arrived in time. - The abstract boundary before the time when I will be late - the action (arrive) in time ON - This preposition creates a relation about contact. Physical relation: The book is on the shelf. - contact - the book (noun) and the shelf are touching The glass broke on the floor. - contact - the action happened on the floor. Abstract relation: My sister has a lot of problems on her mind. - contact - problems contact her mind The light on the wall is beautiful. - contact - light on the wall (is it really touching? - abstract contact) I arrived on time. - contact - the action (arrive) contacts the scheduled time (this one is pretty abstract) I arrived in time, or I arrived on time - have very similar meanings. But as others have said, on time is about contact with a specific time (like an appointment) and implies that what ever happened it was both near and before a specific time, (the movie start time, an appointment, etc.), and in time is about the boundary of time before and up to a specific time in which there is time to not be late, or to do something else.

On time means you arrived right when you were supposed to. Not early or late. It can be used to show that you were not late when someone asks if you were late. Sometimes implying that you were going to be late. (I got here on time!) Appointment at 8:AM EX 1) I arrived on time for my appointment EX 2) I was caught up by traffic but I still managed to managed to make it on time EX 3) I arrived right on time. In time is used usually when multiple activities are involved. This can also imply that you were going to be late. It can be used in many of the same ways as on time but the meaning changes slightly. Ex 1) I arrived at the doctors in time to use the restroom (If you replaced in time with on time in this sentence, it sounds like you made a appointment to use the bathroom at the doctors. Using in time implys that you had an appointment at the doctors but you had to use the bathroom. Luckily you made it there early so you can use the bathroom) Ex 2) I made it in time for dinner.(Even though I had to finish my game) Hope this helped, here is a link that can futher explain. https://ell.stackexchange.com/questions/9623/difference-between-in-time-and-on-time

"In time" is to do something before you run out of time, but "on time" is typically used when you do something at the designated time. For example, if you have a job interview at 12:00 PM and you get there at 11:59 AM, then you barely made it on time. If you get to the interview at 11:45 AM however, then you made it in plenty of time. Having said this, native speakers use "in time" and "on time" interchangeably :-)