This is a hard one. One day would not be enough to fit in everything I want to experience as a woman. A year would also not be good, as I think by that time, I would feel I was a complete woman, and I would not be able to handle having to return to being a male again after that much time. With that I mind, I picked a week thinking it would be enough time to really experience what it is like to be a woman but would not be so long that I would have problems having it taken away from me again.
It is not an option, but the best choice for me would be having the ability to change back and forth at will. I could then get my girl time in but also still be the person my wife married.