I finished leveling my new Rogue. I used Chromie Time and went through Mists of Pandaria. In total, I think it took about 20 hours to get to level 50.
I was able to do four zones of Pandaria: Jade Forest, Valley of the Four Winds, Krasarang Wilds, and Kun-Lai Summit. I was actually just into 49 when I finished Kun-Lai Summit, so I did a few quests in Townlong Steppes. If I remember correctly, this roughly matches the original leveling in Mists. Four zones leveling, and then two zones of questing at max level.
I'd actually forgotten a lot of the details of Pandaria, and it was very enjoyable to see it again. For the most part, the scaling worked fine and felt correct. About the only issue I noticed is that some enemy bleeds did an excessive amount of damage. I didn't use any heirlooms, relying instead of quest gear. I did one dungeon, Stormstout Brewery.
Automatically teleporting back to Chromie when you hit 50 was a bit weird. I don't think it's a huge deal, because you can just hearth back to wherever you were questing and continue on if you want. But it is weird that Blizzard did that instead of the standard automatic quest with a teleport item. Especially since Chromie Time is only for alts.
In any case, leveling the rogue was a lot of fun. Things proceeded at a good pace. I got to enjoy several older zones that I haven't seen in years. Your character gains a new ability or passive at almost every level. The level squish and new leveling is an unambiguous win for Blizzard, something that they really needed after Battle of Azeroth.