Longest: Ibanez Roadster II at 27yrs old. Played the thing to death. First real guitar for me. Suprisingly the frets are still fine, works like a charm. Heck I've got a two year old Ovation who's frets are worse off then that Ibanez.
Shortest. WelI have never sold anything. I keep them all. They all got a story, but I do have another Ibanez from 1990, EX Series, that I just can't stand and knew it within weeks. It has sat unplayed for 22 years. Not sure why I never bonded with it.
I agree that it takes time to know a guitar. Some you know right away, some you don't. Believe it or not my first PRS and only PRS it actually took a few weeks before I was %100 in love with it. It was like it had to break in a bit.