I've never used pig fat, but have used bear fat for this purpose. I had better results than just leaving elm staves un-treated, but it still didn't save all of them. I didn't try to push it and see how soon I could use a roughed-out stave, I still waited a year or so. If you want to see how long it takes them to dry, get a kitchen scale that can weigh down to the nearest gram and weigh the stave every few days until it stops losing weight. The weight it's losing is moisture, so once its weight stabilizes that means it's done losing moisture. Be mindful that if you really caked the fat on, some of the weight lost might be fat that sticks to your fingers, to the scale or to other things.