Thank you very much !
It's true that the game requires a lot of concentration. It's hard to pay too much attention to the UI, although I think it can become a skill that you acquire as you go along. If you don't pay attention to the hourglass, you can attack a boss when he becomes invulnerable again and take damage. So we'll have to pay close attention to the hourglass in future. In any case, I hope that players will integrate this difficulty with this philosophy. If not, maybe I could add some sound indicators to complete the UI :)
Anyway, thanks for playing and commenting :D