"If in the Foxtrot I start my Feather Step with my right foot on beats 3 4. instead of 1 2. I am out of Rhythm."
Not necessarily.
It depends entirely on why you did it - for a good reason or for a bad one.
If you did it in ignorance, or thinking that you were in the usual place in the music when you weren't, and expected the usual feather step character to result, then what you did is very bad.
But if you did it in full knowledge, knowing that this would give the feather step a very different character (almost make it a different figure), and that this character is what you intended to achieve, and what you do fits into a greater whole in a way that makes sense, then what you've done is demonstrate a more sophisticated artistic musicality in your dancing.
Obviously, you had better not attempt anything like that until you are very adapt at putting figures in the usual place in the music!