Running a Holy Pally through BfA, it's taken me 16.5 hours so far to reach 48. I've run but probably not completed quite a few dungeons as well. Finishing out the last stretch ret though, can't stand healing dungeons right now. Everyone's just being stupid.
Edit: All together 18 hours and 2 and half zones of BfA. I skipped all the side quests just to finish the story missions to unlock Kul Tirans.