You can also get from 45-50 in about 2 hours by doing levequests in Mor Dhona. I did that for a lot of my DPS jobs mostly because I'm not a fan of FATE grinding. But, yea, as others have mentioned you're gonna have to kill time doing something while you wait on Duty Finder to pop. Either that or try to find a tank/healer friend to level with for faster dungeon queues.