I recently found the time to pick up Rogue as well (which was the last battle class i could level) and i can tell you that it took me roughly 1 ½ hour to level from 22 to 25 through dungeons (2x Halatali and 1x Toto-rak without fully clearing the dungeons, just by attacking the packs you find along the way). If you craft your own gear, it takes about 2 dungeon runs within a similar level range to fully spiritbond them, so you can generate some materia with it as well. (^_~ )

Also, if you use Food, you can get an additional 3% experience bonus. It doesn’t have to be anything special. You can simply bring along something as simple as La Noscean Oranges, which will only give you that 3% Experience Bonus but no stats.

And also, like Moqi above me mentioned, the Challenge Log also gives a good amount of Experience as well as the Hunting Log.