In 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.
On time
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.
"Sitting" is dubiously "an activity", so the distinction is pretty much non-existent, but if you're splitting hair, seated is a passive form, used in context of state, as opposed to activity. There is no practical difference although you'd rather write about lazy, comfortable way of sitting as "being seated", and attentive, firm, active as "sitting".
There is a significant difference though, if "he was seated by someone". That means he sat down there following someone's direction. You could say:
"We were seated in the first row of the theater by the usher"
It means the usher guided you to these chairs and asked you to sit there.
"We were sitting in the first row of the theater by the usher"
means the usher was sitting in another chair, next to yours.
The person may be implied. That means the original sentence still may imply someone seating "him".
He was led to the front row and seated in front of me.
And yes, it does create an ambiguity.
"You were seated by the exit"
doesn't mean the exit told you to sit, but that someone told you to sit next to the exit (or that you were just sitting there). And if instead of "exit" that will be "the guy selling pop-corn" it becomes quite unclear, whether someone told you to sit next to that guy, or that guy found you a place to sit.
Best Answer
The outcome of the two statements means the same thing (a long time passed) but there is a different inference.
There could be so many different reasons why you were a long time. Maybe you got delayed by something or someone, or maybe you created the delay yourself.
"Take" is a verb and the action is your own. If you took a long time it implies that you deliberately took your time, perhaps lingering, taking a detour, or just acting slowly.