Actually less than 10 minutes if you do a gem only run for purposes of buying compasses. Just run though and kill evrerything and leave. Half the time if team of two and go opposite directions
With gem runs only I used my lv 32 Mightofoaks on Lv 28 Challenge and averaged 4.5 minute runs with complete clearing.
The path I used was go left (East). At 4 way turn left (North), do the circle back to 4 way (make sure to take out enemies in northern pocket), Turn left (South), Follow until you hit southern pocket where Progenitor Crystal spawns (Southern pocket), Continue to far west and head north, At first Left (West) take out enemies there but continue North past western entrance from main room, At far north make sure to clear pocket, Turn right (West), AT west with pockets North and west turn Left (South) 1 "room", Turn Left (East) 1 room, Turn Right (South) 1 room, Turn Right (West) and follow to bowling alley, Turn Left (East) thru waterfall, Continue East for 2 Groups of Mobs, Turn around and come back 1 room and turn Right (North) for last group of Mobs.
Note: Since you are not going for XP (no completion), running this over level makes no sense. Run it for the level of gems you need and that will actually drop. Since there are optimal levels for gems this can be used as an argument for having alts at those levels (I spent 14.5 hours trading Stolen Gems this past Crystal Cove, I played videos when tabbed out of DDO but came back every 10 minutes or so to check progress). The use of wings/leap ability makes it faster. Remember you can regain SP at the shrine at the beginning. Killing the Red Named monsters got me quite a few Requisitions/other drops.