Levelling your first class even with MSQ I think actually takes longer than any of the classes after it. If you have food, an fc for the exp buff, and have some rested exp saved up, you can go from 1-50 in a single weekend if you really wanted. 50-60 was made faster with 3.1 now that the heavensward dungeons give better exp, not sure how long they would take now but it took me a week on smn waiting on dps queues (everything else was spread out just doing my roulettes so I cant use them to judge time taken).

You only need to get to 10 to switch to rogue (providing you start in limsa, otherwise you'll have to reach it first obviously) and whatever your highest class is is the one that wont have the armory bonus. Anything lower lvl will get increased exp. Just start as pugilist, get it to 15 so you have that ready to unlock ninja later, then go to limsa and unlock rogue.