On day 4, 100 harpies arrive in the city of Kiffa, and I understand that I need to conquer the city by day 3.
Wait, are you referring to the dungeon near Lorelei? I call it Celle...
I took resources as a starting bonus - 10 stone and 10 wood, after which the city is captured in 1 day. The author likes to "borrow" such things from other maps; I think this is taken from Rise of the Sun.
As I already wrote on YouTube, I didn't play this map any further.