it depends on your goals. if you are wanting to reboot they recommend 90 days, that's why you see that all the time. my see my goal is totally abstinence, but I have a 30 day goal to keep me motivated. a good place to start is by doing one of the month challenges, but either way figure out what you want to do and see your challenge accordingly.
It depends on your goals and what you hope to accomplish. Its safe to say that most people that successfully complete a difficult NoFap challenge will realize the harm that porn has caused in their life and as such will stop fapping for life. As for what that first challenge should be, it depends. If you're trying to fix erectile dysfunction or delayed ejaculation, you should probably do 90 days without porn or fapping before you try having sex. If you're curious about the effects or think you might be addicted, try for 30 days and go from there. All that being said, its still entirely up to you.
90 days is an arbitrary number we made up that serves as a solid baseline for rebooting from porn addiction. If you grew up with internet porn or have been using it for a while, rebooting will likely take you a bit longer than 90 days. It really depends on the Fapstronaut. I'd shoot for 90 days and then evaluate where you stand. If you feel like you are not fully recovered, give it another 90
Hey man I would start with something that challenges you. If it doesn't challenge you, it won't change you.