What happens to me is that if I don't touch a track in a week, then I will probably never touch it again. With that said, the longest time it's taken to make a track has to be:
According to my AIM logs, we started it on September 25, when Neodrummer sent me over a melody. Then, from there, I did the rest, submitting it on November 1, completely finished, for a grand total of... 1 month and 5 days from conception to completion. Not bad.
However, the song that Chim and I are working on now is much older... I started it on September 9 as a freeform track, then we slowed down the tempo to make it Hard Dance. It's still not done, but we're working on it :P