It depends on growth and attrition. At regionals, movement is normally faster because people leave for other jobs. If the industry is doing well, you might have regional growth and attrition at the same time, and might get to "good' seniority in less than a year (good seniority probably being better than 50% in your bidding position).
But you could also sit reserve for 20 years at a major if there's no growth ...few people ever leave majors, so you essentially have to wait for people senior to you to retire.