I have an appointment at 8 and I arrive there at 7:55, is it "on time" or "in time"? What about "the nick of time"?
Suggests that you arrived, or accomplished the desired task, at a time sufficient to be effective. Typically, this means "at or before a deadline."
We finished cleaning the house in time for the guests to arrive.
In time to...
A related variation on the phrase "in time" is "in time to" (also "with time to"), and indicates that you arrived or accomplished a task with time remaining, sufficient to do something else.
I finished cooking dinner in time to take a shower before the guests arrived.
We got the kids in bed with time to watch a movie.
Suggests that you arrived, or accomplished the desired task "exactly on schedule."
I arrived on time, at 8:00pm.
Although, the phrase "on time" is often used interchangeably with "in time" and it is probably rare that you would find a context where only one would be understood.
"In time" means various things but here it would mean with time to do something. So, something like: "My appointment was a 8, but I arrived at 7:55, in time to wash my face before the meeting".
"On time" means that you arrived when you were supposed to: "My meeting was a 8, but I wasn't exactly on time, I was 5 minutes early".
"In the nick of time" means without any time to spare. "I boarded the train in the nick of time, just as the doors were closing".
I believe that on time means at the planned time: neither late nor early.
For example, say you have class at 8 a.m., and you show up at 8 a.m. You would be on time.
However, in time means with enough time to spare.
He is lucky the ambulance arrived in time. If it had arrived any later, he would have died.
"On time" implies keeping fixed schedule; example, if the office hour is 8:00 am and you always arrive in office at 8:00 am, then you are always on time. It also means keeping a planned schedule.
"In time" implies an event that was not planned or scheduled,example, if rebels are about to kill someone and you arrived just at time of killing the person, then you arrived in time perhaps to save the person. Another example could be, the doctor arrived in time to save the dying patient.