How long after going pro till you get the Buy box / Featured

I’ve been selling on Amazon for years. When I signed up it said only go pro if you sell 40+ item. I sell custom made items that I make and are unique. I only sell afew a year. I’m looking into increasing sales. How long after going pro FBM till you get the Buy box / Featured? I saw some places saying 3 months? But paying $120 for maby getting doesn’t seem right.​ what i sell is neech and I’m not sure if I’d even get 40 a month