When is the optimal time to leave for the island?

[Roman]

I am a level 7 Mage now and have the option of going to an island to prove that I am powerful enough to the king. This is the quest after the Chests of Rage. When is the optimal time for me to go to this island? Should I go now, or wait until I am stronger? This quest has been available to me for some time now, but I have kept roaming the main continent to get stronger first, but I am not sure whether that's the best way to do it.