Well I guess they have figured out that's how long it generally takes. I'm pretty sure they didn't just pull the number out of their ass. I think the general idea is to stop for good, and 90 days is just how long it takes to get your brain back to baseline.
If I recall right, its set to 90 days because that is how long it takes for a brain to re-sensitize after a chemical drug addiction. You are not healed, just rebooted. Healing may take up to 2 years to get to 100% from what I have read, though it is non-linear, so in 6 months you may be 90% healed, 95% in 1 year and 100% in 2 years. Depending on your condition obviously.. In other words, stay away from Porn and Fantasy.
90 days is a challenging period of time but ultimately one that should be doable and just far off enough to see it. I'd focus on 90 by doing step ups first; 1 day, 7 days, 30 days, 90 days. Obsessing towards 90 days only will probably make relapse much more likely.
"If I recall right, its set to 90 days because that is how long it takes for a brain to re-sensitize after a chemical drug addiction." So is it a comparison to how long long it would take to recover from a cocaine/amphetamine addiction for instance?
Maybe physically, but really recover from an addiction? No that is a lifelong process. There is no way someone can mentally recover from a real addiction like that in 90 days. I've been off drugs for a year and still far from perfect.
I agree with Chris. I quit smoking 15 years ago, but I'm still addicted to nicotine. And always will. I expect it's the same with PMO. You may rewire the brain to the point where you no longer have the symptoms that made you stop in the first place, but if you let your guard down, you can end up right where you started in short order. This is a life-long battle. (But don't be discouraged. It does get easier. With each day you distance yourself from it, the easier it is to take the next day. And after a while you learn to avoid it, and live without it altogether).