Does the sexual orientation of a sexually fluid person usually change more than once? If so how long does that orientation last before it changes again?

There are no expiracy dates on sexualities. It's very subjective and variable. Plus, though the degree to which one person is attracted to one gender or another can vary in time, if a person could be potentially attracted to more than one gender, they would still fall in the bisexual spectrum. So the orientation doesn't change, it's the degree of attraction towards one or the other that fluctuates.

Yes it can and there isn't any rule about it. If you're sexual orientation is fluid, or if it's bi/pan with period where you're more attracted to certain genders than to others, well, there is absolutely no way of knowing when it can switch, how it can evolve etc. In fact, that's true with anyone, of any sexual orientation. ^^" We're not robots. We evolve, we change, we adapt, and we can just find what feels good at the moment :) Hopefully, you're attracted to people before their gender, so if you're with someone (or some ones if you're polyamorous), your attraction toward them will keep the same, won't it ?

There actually is no answer for this! It ebbs differently for each person. Normally, if someone is “sexually fluid”, that could mean bi or pansexual. In these cases, their orientation doesn’t actually change. Their orientation is “being open to love regardless”, so they just love whoever they love, for the time they love them. I’m bi-sexual and have been in a “hetero-seeming” relationship for 2 years, and I imagine it will last a lifetime. I am still attracted to women, but I don’t intend to be with anyone else but the person I’m with now. So, this doesn’t mean I’m straight now. My orientation doesn’t change, just my relationship status. (: Hope this helps!