Junior / senior / staff titles are typically used for HR to justify a lower salary (typically called pay band) . It artificially suppresses your salary even though all roles do extremely similar work.
I'll say it takes 3 to 18 months to become a domain expert at a company depending on the scope, if you are fresh out of school. Less if you already have relevant experience. And then years to become company/subject expert, and those you have to pay to keep them.