Dude, the problem is that Nebiros' growth is incredible...
How long do I have to wait? After 15 months, I went to him, and he had 10,000 lilies, a thousand broodmothers, etc.
Plus, when capturing Gustav's stronghold, both humans and demons react inadequately...
Before, they just passed by, but now they show up with a huge army there...
You need to capture enemy castles and rebuild them into your own as quickly as possible.
Nebiros can be defeated as early as the fourth week.