It's unnatural and very akin to the people who advocate extreme diets to "reset" their metabolism. Not to mention it's basically saying "Stop being a porn-motivated maniac.... for 90s days, and then become a sex-motivated maniac!" The stuff about "breaking the craving>gratification processes" is absolute rubbish. That's like saying you're going to "break the hunger>eating processes" for a diet. The addiction may take the nature to extremes, but it is still the nature of humanity to crave and fulfill.
The 90 day abstinence concept teaches nothing about true understanding of oneself, the realities and virtues of moderation, the intentional direction of sexuality as a self-moderating activity, the role of sexuality in relationship to others, etc. All it does is subject a person to a needlessly harsh refrain to more dramatically show a person that their addiction was unhealthy when it could have been done more moderately over a greater amount of time and result in far more self-awareness, command of sexuality at will, and truly understanding human nature in the connections of sex, sensuality, emotions, and relationship.
Really, the correlations to diet quackery are pretty extensive.
Did I not say already that I had done it before? I was very religious most of my life, I have plenty of stints with abstinence and self-analysis behind me. This one-step miracle fix stuff is all a load of shit. People only notice a "big change" without having a proper understanding of anything. You should read stuff on sexuality other than this to realize how small a scope it is actually looking through.