I would say the first hell rank is rank 9, but really should take about 13hours nonstop chopping. The first real hell rank I would say is rank 6, simply because you can't rank up just from making the wood and bows, you need to chop 11.00 worth of exp, with 0.04 for average, and 0.10 for fine, so it'd take a while.
At rank 4 the difficulty jumps, because of the "Successfully create Fine Grade Bow. ", which you have to complete 25 times by spamming Short Bows (assuming you finished the other requirements excluding 1000 Fine Wood). On average on mondays, I was making 1 "Fine Grade Bow" out of 10, so you can see it's a lot of spamming. A "Fine Grade Bow" basically requires the description to say "A bow of godly qualities has been made", (it'll be sigged and +2-3dura)
Subsequent ranks, though I haven't reached them yet (still on 4), the number of "Fine Grade Bows" required to rank up becomes less and less.
Hope this helped, correct me if I'm wrong please ^^
I got a lot of work ahead of me