with cornish, it depends on where you buy them, what you feed them, how you house them, how fast you want them to grow.
Me
Sunnyside Hatchery, WI the best chicks that I've found (I've tried alot)
Feed, my own recipe that the local coop mills for me, its the same feed I give my chicks & turkeys, I do not restrict feed ever
Housing, Semi-free range, coop till 4 weeks then allowed to run the yard with the feed and water out side the building at least 50 ft apart, makes them move, and graze, also they can control how warm or cool they are by sunning or going under the trees
my 8 weeks are usually 10 weeks because we want 5lb+ chickens
I have never had leg problems, sudden death (flip) or any other problems that can occur with cornish, since I started to use this system