Thanks, and to correct my previous post it's been more a lot of sweat than a lot of sweet!
I made the Anga Ruby quest by using fast travel. When you lost a standard battle you take secret passages that lead you to Darion King castle instantly.
The problem is you don't carry your army with you and have to rebuild a full army. Quote that you could let all troop in castle and then use this special travel at next enemy met without to lost a single troop.
In this game I used this at end of Elven Islands. I did last battle (Karador) in time, let troop in both elven castles and fast travel to Darion. I had let close to Elven Queen Castle an enemy troop alive not far. After I took the boat to Freedom Islands, rush to ghost ship, end the quest and took the reward and asap did again fast travel to come back to Darion then I rebuild my army and continue.
I did this only at end of Elven Islands because I hadn't prepare full army rebuild at end of Freedom Islands. But that could be done at end of Freedom Islands too.
That's quite more complicate to do it in 6 days. But I think it's possible so I'm on it with a game restart from the beginning to prepare this well.