Thank you for the kind words! Swords and Deviltry was probably my most recent Appendix N read, so it's influence on this project is very likely.
It's always tricky to know how hard to make puzzles/riddles. I've tested this one on a group before and they did alright with it, but I'd be interested to hear how it goes for others. I can definitely lengthen the timer or add extra hints in future updates.