GY Rampart played Champions of Gelia on Easy difficulty in 22 days. DD (Dungeon Door) was given in the Red City to Rampart. He made almost no unnecessary moves. When the 3rd hero jumped over the mountains with the DD, he was in such a hurry that he didn't wait for reinforcements that were twice the size of his army, even though the hero with reinforcements was only half a day away. He started with Kairic (Logistics), and you can buy any mage with Wisdom in the tavern in any city; I bought some bearded guy from Rampart, I don't remember his name. I tried to replay, and I started returning the hero for the DD to the starting city 2 days earlier. I did everything better, but it still took 22 days.
By the way, the DD is not needed in the starting city. Since you still have to capture the Red City, and you would have to return anyway. So, I captured the Red City, built the DD in 4 days, and in 2 days I took the Pink City and won.
I think that it is possible to play on Impossible difficulty in 30 days. I will rest a little and play later. It is impossible to play this map faster than 22 days on Impossible, I think modestly. Although, there may be pros who can do it.
Added 2 minutes ago
P.S. try playing with a configuration of 200+ Gryphons and 50+ Storms; on the second turn, they will crush any army of the stupid AI! Preferably with a Cyclops or a Grindstone (due to the slow start and Earth).