The generally accepted time frame is one hour per inch of thickness. When I steam them, they're usually about 3/4" thick near the dips and 5/8" at the tips for a flatbow, but I still leave them in there for an hour... or an hour and fifteen minutes if I have serious corrections to make.
No, don't soak them. It's nice to do them not long off the stump while they still have a good amount of moisture in them, but I've never soaked one and never had an issue.
How far they will spring back after releasing the clamps depends on several things... the kind of wood, the degree of correction, how hot and pliable the stave was when the correction was made, how long it's left clamped to the caul, how much moisture is/was in the stave, stave dimensions, etc. But generally I over-correct about 10%.
I steam them in a 4" stove pipe, then remove them and work on them with the caul held in the bench vise where I can work all around them efficiently and effectively. On crazy osage staves, I've used over a dozen pipe clamps and c-clamps on them to correct twists, humps, whoopdy-doos, and limb alignment... all before it cools. Cut yourself a bunch of 1/2" plywood pads to put between the clamps and the stave so you don't dent the wood. Have a plan, everything needed within arm's reach, and work efficiently. There's no way I could pull some of those jobs off inside a box like Del mentioned. I've had clamps sticking out all four sides. The box would have to be bigger than a coffin.
