Beating RoV has no effect on the creation of an Ergon Weapon.
Information about how the KIs can be obtained is found at the bottom of the page here:
https://www.bg-wiki.com/bg/Reja_Ygridhi
You obtain the KI that lowers the timer to 5.5 hours per KI after you have spent 100 imps in each coalition. But prior to that it is 6 hours each. Any further reductions to the imp timer are unable to be obtained until after YOU ALREADY HAVE LEGEND IN EVERYTHING (fucking SE.).
6 coalitions x 100 tags x 6 hours = 150 days
+
6 coalitions x 40 tags x 5.5 hours = 55 days
Meaning it would take you a total of 205 days (or 6 months and 3 weeks) to do all of the coalitions from scratch if you do it in this specific order. And people wonder why I complain that they need to lower imp timer so much...