I have a Hornady L&L. To change calibers with the assumption that I am also changing primer sizes and shell plates I can probably do in under a half hour.
First I would screw the dies out of the press bushings and replace with dies for the new caliber. That only takes maybe three or four minutes. Then I would change the shell plate which takes another two or three minutes. My next step would be to adjust the powder measure Case Activated Powder Drop system. This requires my weighing test charges and making adjustments for same, and it may take me ten to fifteen minutes to do it. Adjusting the dies would be my next step, and that would be maybe five minutes. My last step would be to change the primer tubes and shuttle. My primer system works real well, so changing primers is certainly less than five minutes.
Those steps for me add up to about a half hour, and that may seem long to a lot of folks. It really isn't for me. I could use the L&L bushings as they were designed, but I really do not like doing that, and it really does not take long to change dies. I also like to adjust my bullet seating die and case mouth belling die each time I use them. I guess I could also get a different powder measure and Case Activated Powder Drop system for each caliber I use to save someone else's idea of valuable time, but I load for a lot of calibers, and I cannot afford to buy different powder measures and drop systems for each. Besides, I would still have to spend time weighing a bunch of test drops either way, and that still takes time. I don't know how I could make changing primer sizes go any faster than it does already. In addition to all the other stuff I do, I forgot to mention that I probably would take a trip to the head for another three minutes before starting in reloading a new batch.
I don't get lost in the idea of how fast I can change dies or even how many cartridges I can load in an hour. For almost forty years I loaded all my metallic cartridges on a single stage press. When using my Hornady L&L, I am perfectly happy with the idea that I get a finished round with every cycle of the handle. When starting to reload a batch of cases, I know I can expect them all to run through the press without having any stoppage. As long as I keep my press clean, it is a rare occasion when I encounter a stoppage. If I can take my time and still load five to ten cartridges a minute, that sure is fast to me.