If you mark runes in the right spots you can go around and around 6 times before the timer runs out...What I mean is once you do the Quest once, you can start back at 'Grizelda the Hag's' Place and get another Soul Harvester and then recall to Deceit. At Deceit, it is the best of both worlds, as Moongrass grows inside the Dungeon and once you get the 4 Corporeal Residue, you can change into monster form right there and not have to recall anywhere else. Gather up the souls til it is full, recall to the Hag's Place, turn it in to get a Crystallized Essence (a lot of Essences in the game now), then grab another Soul Harvester while you are in Monster Form, recall back to Deceit and gather souls as fast as you can...Rinse and Repeat...! On 2 runs tonight I got 6 Essences (3 Blue, 2 Red, and a Yellow)...
My guess is you need 30 Blue ones to get a Cloak and 5 red ones to get a better costume...
The yellow one I have not used yet...!