I only went into the Dungeon when Kahn arrived.

..well, then yes, it's too late... you need to swim there immediately and not waste turns collecting resources. Then, on the first day of the second week, you'll already capture the Hunting Grounds... then two mines and rush to the Witches' Hut and immediately to the portal to the city. Let others pick up everything later... put idlers in a chain to the Fortress to upgrade Invisible units... don't take Groves until the very end of the game, that way you save a lot of experience... just run around the Arenas and Temples... that's how it was.