That *HIDEWORKING* calls your characters hideworking skill. The %20% adds 20pts to your characters skill. So with skill 20, you have a slim chance of getting fine shoes; when crafting from fine or superior leather. With skill 50, your character has a slim chance of getting, masterwork shoes, IF crafting from superior leather. Somewhere around 50-60 combined skill (not sure) you won't get any harsh products. (except if using harsh materials)
and that /90/ is the time, in minutes, it takes for the recipe to finish.
If you'd add [noquality] tag on a recipe ingredient, that would allow lower level to produce higher level goods. Apart from timber, I'd say that's cheating. But it's your game, play as you want to.