How long should a successful rebuild take?

Saints did it instantly after 2005. The nfl.is a bell curve. There are 3 or 4 excellent teams, 3 or 4 really bad ones. Then there are on either side 5 mediocre teams. Then the rest of the league the teams are pretty much equal in overall talent.

So with the exception of a couple teams a rebuild can happen very fast. Miss the playoffs one year, make it the next and be a really good team.