I normally move them every week. One of the sows had babies when the barn was already full of babies, then one of the pigs in with her killed and ate a baby (she kept laying on it - I heard it squealing but she wouldn't get up and the mother didn't chase her off, for some reason). So I had to sacrifice a paddock to put the other pigs in to keep them away from the little ones until they were bigger/stronger.
The bare paddock that resulted was planted with corn, squash, pumpkins, and field peas, and I put in 12 apple trees around the fence line for shade and free feed in years ahead. They'll need to be protected when the pigs are allowed back in again. I also underplanted with clover, for next year's pasture. I think it will slowly grow among the other plants then really take off when they're removed. I like the irony that the paddock will provide us with pork and the applewood to smoke it with!
What I'm seeing is that, due to their rooting, the stocking rate is much lower this year if I want to keep to the same rotation schedule without them destroying too much of the paddock's grass/clover. I figure last year they were in each paddock for a week about 6 times. If I plant the paddocks and then let them in to "harvest" they'll only get one use out of them when the crop is done, unless I can manage some sort of seasonal rotation, like ryegrass after they demolish the corn stalks. Hmmm. They really like ryegrass. That might work.
My comfrey is huge this year, so I think in the fall/winter when I move the pigs off pasture I can harvest the roots and plant them in the paddocks, but with 6 weeks in a paddock, wouldn't they just destroy any comfrey that was trying to grow there, even if the weeks were separated out so it was only 1 week a month in each paddock? I think the Jerusalem artichokes would work the same way - they'd dig up every last root and eat them then keep rooting there so the plants couldn't re-grow the rest of the season. It seems like it would be better to have a separate, "fall paddock" where the comfrey and Jerusalem artichokes could grow all summer to be harvested once in the fall, leaving some to re-grow the following year. But out of 52 weeks in a year, that would only feed them for, what, a week or two? And be out of the rotation for the rest of the year?