I hit 20 last night. I logged out and logged back in to see how much time I’d played, but I guess Blizz got rid of that feature. I think it took me about a week, maybe 7 or 8 hours. Some of it was with rested XP, and some without.
Next stop is my mount and then I’m going to stay in the Barrens area to grind out my leather.
 as noted by the super-cool Poster below, you can access that info by using /played. It took me about 11 hours. Longer than I thought, but I did do some monkey-ing around in Orgrimmar a few times.