how long does it take to level to 64?

[Caimie_Tsukino]

That's a very difficult question to answer, depending how you level them... I guess the fastest way would be leves? But lvl 51-59 leves requires access to Ishgard, and lvl 61-69 leves requires access to Kugane... So your MSQ must be up to those points.

Please DO NOT straight up gather stuff to level up, it takes FOREVER... At least make use of Survival Manuals and Food to boost EXP. It's best to have resting bonus EXP as well (gaining from logging out in an Inn or FC house).

Diadem (from the Firmament) is also a reasonably fast way to level up while earning a huge amount of gil, but you need access to Ishgard first again (and please bring along your Survival Manuals/Food).

Grand Company Provision Missions are also a great source of EXP, but you can only do those once a day.

Collectables are also a reasonable way to level up, and these give you scrips which you can use to buy material / Hi-Cordial / gear.

So I think you should at least get your main battle quest to go through all the MSQ at least up to the point of reaching Kugane.

Also, personally, I find it best to level MIN and BTN together if doing leves, because the leves of their locations are very close by anyway. So why not grab both together from the same NPC, and do them together while on the same Survival Manuals/Food in the same region... all at once.

Assuming you have access to everything mentioned above, leveling 10 levels can take about 2 days' work to a week's work (depending how many hours a day you play).

[Yuyun]

It's best to have resting bonus EXP as well (gaining from logging out in an Inn or FC house).

Just to add:
No need to log out in an inn or FC house. You earn resting exp in every sanctuary - either a Camp, City or housing ward. The chat tells you when you enter one and you have a little crescent moon icon behind your exp bar.