Board Thread:Questions and Answers/@comment-26359879-20150508000003/@comment-26215551-20150508001503

Tantous are actually 0:20:00 (or 0:30:00 in the case of Atsu and Hirano), and Naginatas are 5:00:00; all of the Smithing times can be found on the smithing page. There are general trends, but rare swords (aka swords that are national or imperial treasures in real life) will have slightly longer smithing times. e.g. Hotarumaru has a 3:00:00 timer instead of a 2:30:00 timer like other Oodachis, and many of the rare Tachis have 3:20:00 timers.

In the case of Kogitsunemaru, he's technically only 3 stars in his listed Rarity, but he's very hard to obtain, as he rarely appears from Smithing, and only drops from 5-3 Boss Node and a few spots in 6-1. Combined with his nice personality, it's clear to see why a lot of people want him.