It's a 10 gp magic item, it should take, at most, 1 day per bandage, because of the 1kgp progress/day thing.
Also, it should take 13 weeks to make a masterwork composite longbow for an average craftsman...
And what reference is your DM using for that bow time? I've only ever seen historical accounts of infinitely less time than 1 year for a good longbow...