Hello there,
Here's some insight on your topic about the range, 99 range at rock crabs using iron knives will be HORRIBLE. I wouldn't wish that upon anyone if you are going to use knives atleast go to the cages orgs in the training ground you can use a cannon here as well to boost EXP. As far as length in time? I would say if you play 5-6 hours a day it would take you about a month and a half... I would HIGHLY recommend that you chin I know it costs a bit but it is much much much faster I would say it would take you about 2-3 weeks at 5 hours a day. It's really up to you, do you have the patients to take like a month and a half or 2 months for 99 range? If so then my hat comes off to you. I would honestly chin, that is your best best.
Good luck on whatever you might choose to do!