EDIT: Actually, I just took a look at the craft rules. A quiver with 20 arrows costs 1 GP (10 SP). Making bigger arrows costs twice the price per size category (so 40 SP if going by standard math or 30 SP going by D&D math). We want only three, however, so the cost is reduced to 3/20ths (6 SP for standard math or 4,5 for D&D math). Assuming a regular craftsman can easily make the DC 12 check, with progress per day, we have 12 x 12 = 144 (potentially more, assuming he beats the check result by more). 144/7 = 20,5; which is roughly 3.3 times 6 or 4,5 times 4,5. So at an absolute minimum, a craftsman takes... 8 hours to produce three Huge arrows? Well, assuming the minimum result anyway.