It all depends on where the characters are in their rotation when you are seated. We always do lunch. The least amount of time we have ever spent at CP was 45 minutes, and that was because the first character in the rotation was almost to our table when we sat down. We sat there and got through all the characters quickly before we even went up to get food. The longest we have had it take is 2 hours- that is because we had to wait quite a while to be seated. We had the first lunch time and they would not seat anyone for lunch until all the breakfast people cleared out that year. Typically, I would say normally it runs between an hour and 15 minutes to an hour and a half.
I would also note that back when Pooh and Tigger met at EPCOT too, the lines didn't seem as long when we would see them at Magic Kingdom. Seems like the lines at Magic Kingdom got a whole lot longer when EPCOT got rid of their meet and greet a couple of years ago. I'm not sure how the new movie might be impacting the lines right now. If you go that route, definitely plan it out ahead of time and don't just show up in the middle of a set, or you could wind up not saving that much time by skipping the character meal.