Depends on what you mean by sellable size. If you mean taking a bunch of 1"- 1.5" fish to a LFS and getting 35cents each in credit (what my LFSs would usually provide) probably not too long.
But if you mean 3" good looking specimens, that could take a good 9 months, and would mean separating out sizes into many different tanks so the fry don't kill each other, or putting them all in a kiddy pool to grow out , with lot of water changes, and lots of food.
I especially like putting fry outside in the summer where they can get plenty of algae, daphnia, and other Iive food to graze on all day, then scoop them out at the end of summer when they.ve put on size.