1) Have everyone equipped with as many different color spells as possible in the low-end of the element grid.
2) Get everyone's stamina to 7.0 with their element thingy to 8.
2) Let the Time Devourer do the first chime for you.
3) Knock off the elements as quickly as possible using as low-end elements as you can.

Simple enough really; you just need to get the tactics right.