Unfortunately, 20-30 mins is about average for a dps queue in the low level dungeons. I think melee classes are a little faster, but ranged typically has the longest wait. The best thing to do while waiting is FATEs. Once you get to lv45 there is a quick way to get to 50, about 2 hours depending on how many breaks you take. And that is doing around 50 or so leves in Mor Dhona, over by St. Coinachs (however it's spelled). Do the Grand Company levequests and the normal levequests. They will take 3-4 mins each at lv45, getting shorter and shorter each level until level 49 where most of them take about a min. (there are 2 GC leves that are a mandatory 5 mins, I usually avoid them). Same exp as fates in a fraction of the time. I've done this for most my classes, it's a lot faster than waiting for dungeon queues and even fate grinding.