1) The Eastern Castle is captured earlier than the Central Castle (on day six if you hurry);
2) There are many unguarded mines near the castle (including a gold mine!);
3) There is an opportunity to eliminate all demon activity in the northeast.
I put the plan into action. This time, I slept soundly :) Here's a brief description:
111. I build the Enchanted Forest, buy 10 Dryads. I buy two Heroes: Gilraen and Anwen. Faidaen takes the mine and the resources near it. Gilraen takes the army from Faidaen and captures the lumber mill and the wood nearby. Anwen, with 19 Dryads, rushes north to capture the mercury mine and the crystal mine on days 112 and 113. We build a ship. Faidaen takes the campfire and boards the ship.
112, 113. Gilraen returns the army to Faidaen. Faidaen sets sail and, without being distracted by the treasures of the sea, sails to the Eastern Inferno. Gilraen gathers resources. Anwen takes two mines and aims to break through the demons guarding the resources. (In general, three stacks of demons are easily (but slowly and tediously) defeated by 1 Fairy. Even four stacks are sometimes defeated, but here the role of morale increases for the demons).
114. Faidaen is on the shore!
Thus, it was possible to capture the mines, except for the gold and gem mines, and also to sail to the Eastern Castle in the shortest possible time. Two birds with one stone. This is much better than arriving at the Eastern demons on the fourth week and seeing Alastor with 4 Archdevils, 10 Pit Lords, etc.!