In my experience with oil pulling, using flax seed oil was the best at softening the heals of my feet. Mine get really bad in the summer because I wear flip flops all the time or go barefoot.
Check out the oil pulling forum and ask any questions there. Molly is a great help with many others successfully using oil pulling.
I think you would see quick results, like in a week if they are really bad maybe a little longer. Also eat a tablespoon in the morning and one at night. It can be pretty strong tasting, just chase with some juice or water. good luck!