You will have 20 minutes to kill him, so the ideal is to leave and enter the room when the boss is low on health, so the time will reset for the second time you entered. Ek can take the boss to the south and trap in diagonal, from the second jaul everyone must make their familiar summons.
Depending on the amount of people on the team it is possible to kill 4~5 jaul.
Example: with a team of 5~6 people lvl 200 it is possible to kill him 4x.