Hey I actually did that in my uni years because I wanted to experience manga in the original way. I guess it depends on how fast you absorb stuff like vocab but if you’re already used to listening to Japanese convo, it could take a few months to master the grammar (that’s the easy part imho). Then the hard part would be the writing (which you could avoid entirely since you’re focused on anime but I don’t think it’s a good idea in the long run since there’s a lot of written stuff in anime as well) and vocab. If you study a little every day (say 1 hour), it would take 6 month to understand basic stuff (like teenage shonen) and then a few years for more advanced stuff. That’s just my two cents In my case, took me 2-3 years to actually read shonen manga but I still struggle with furigana-less manga