I have not worked on a project that long, but I am thinking it might take you four or five generations to get a sort of "more cochin than not" variety going. I have been working on my Barred Bearded Olive eggers now for three generations and they are FAR from looking like an actual Ameraucana, leg color aside. They still look like mutts with beards and pea combs and varying amounts of barring. That's without throwing in Lavender. I do have a couple of blues in there, but that is easier to work around because you know you have it if you can see it.
The start, probably barred rock x ameraucana
From that hen, crossed on marans, I saved out a roo that had a single barring gene and three black pullets, pea combed and one was bearded.
Some had single combs, some pea combs
Some of those were crossed on a blue marans, most were crossed on the single barred EE roo.
These are F3. Still some single combs. There were a lot of non-barred chicks, which I did not choose to continue on with.