It can take an instant, if you’re willing; it took me a couple years because I wasn’t. When I finally became willing, things shifted very quickly.
For me, it had everything to do with the two-sided coin of: 1) self acceptance, and 2) unknowingly needing something from someone else, that being “acceptance”. When I came to understand that it was my job to accept myself, the opinions of others just didn’t matter.
I’ll use a crude, oversimplified, yet common, example on purpose: I feel insecure about how sexy I am. There are two people in front of me that have an opinion; one I feel attracted to, and another I don’t. With the latter, the one I don’t care about, they can say whatever they want, but I’m not putting my acceptance of myself in their hands, simply because they don’t mean as much to me. I have the ability to not take their comments personally, because I don’t value their opinion. For the other who I _want_ to like me, if they say “ew, you’re ugly”, I could take that personally because I’m giving them some authority over my sexiness.
If I’m in a healthy place of acceptance about myself, they could say I’m ugly, and I could easily not take it personally. Instead, I could joke about it towards having a good time together, I could ask them about it towards learning about their aesthetics, I could agree with them towards more vulnerability, etc…
Of course, as I change and come to know myself more and more, I find more of myself to accept. It’s a process and an attitude. We can’t just say, “as of today, I accept myself and will never have to do so again.”
Nowadays, if I get a twinge of feeling like something is a personal “attack”, I’m pretty quick to realize that it’s more (if not completely) about them, and/or it’s an indication of something I can own more of, take more full responsibility for.