I don't know much about hewing. But, I have done some riving. I would think you would want to work the log green. My reasoning is that, if left on the ground for more than 10 days to 2 weeks some species (oak) will begin to spalt. It is no easy task to throw around green logs either, so I think that working it down closer to its desired dimensions would help with portability, so that it could be stacked properly or worked.