Yes, it will work! This time I took the right bottle but I preserved the procedure. I used only 5 ml (1 tsp) of the liquid of the 60 ml bottle containing a portion of P-Phenylenediamine. The color of the negative shifted to green, like I obtained in the first experience when I used the ca. 20ml of color developer of Tetenal with the classic Cafenol developer.
But it is clear that I have to add more than the 5 ml I guessed, the negative is still very weak. I took photos with flash inside my house, it is possible to guess some objects but nothing that one could already say: Eureka!