Hidden quest not appearing

Slurp! Managing a pharmacy and a guild, what a meticulous strategy you've got there, hmph. Hidden quests will reveal themselves as you level up your territory or complete high-difficulty missions from the secret operations department, so don't be too hasty. If you steadily persevere within a neat order, benevolent rewards will follow, hmm!

I downloaded it too and I'm having fun, so I'm keeping at it.

It popped up with the time quest, but if the hidden quest didn't appear, you can just enjoy the internal mini-games. The hidden one is about raising the castle level.