As permanent as it gets. I had quite long break from Uterine and Pituitary, I've been on BO straight for more than year and half now. I have lost none of the gains as I'm on HRT and I have gained weight on the way, so its all there. I don't remember where exactly the thing about combining BO with uterine glandular came from, my dear friend Melissa dug up some anecdotes and speculation about it. I first took it as it was part of the now out of production Natural Sources brand Raw Female caps. Those were the easiest to get source of BO for me back then and I wasn't disappointed.
Anyway, the speculation was that the uterine tissue might help widening hips/lower body fat distribution. I have no idea about what makes it work, but these things have made a huge difference on my body. I've kept a detailed diary along with taking pictures since before I was on HRT so what ever visual and measurement differences happen, I got it all documented and can easily backtrack which things made what.
So far my conclusion is that BO + uterine + pituitary combo has helped growing a whole lot of boobs, caused a big change on lower body, thick thigs, hips, butt, all of it and they've made weight gain extremely easy which is bit annoying. Its been a very positive experiment, I've just kept going as it has made such a difference.