that's weird, because my experience is exactly the opposite! I've spent about 4 months on my team so far, which has very little to do with my background, and after I realized just how bad the fit was, I started a conversation with my tech lead, his supervisors, and some HR people about moving to a team that would be a better fit (which had openings at the time).
3 weeks of conversations later, I was told that the 18 month rule was "fair" in everyone's opinion, and that if I'm really concerned about working on projects that are interesting to me, I should just find one to spend my 20% time on (easier said than done).
3 weeks of conversations later, I was told that the 18 month rule was "fair" in everyone's opinion, and that if I'm really concerned about working on projects that are interesting to me, I should just find one to spend my 20% time on (easier said than done).